Martian Lessons for Taking Care of Earth

By: Richard (Rick) Davis, Laura Ratliff, Logan Brown, Bob Collom

When we embark on the first human expedition to Mars, we will not just study that planet–we will improve our ability to care for the Earth, too. Sending scientists to the surface of another world will help us piece together the details of Earth’s climate and geological history, which can help inform its future. Yet, going to Mars will not be easy. The challenges of limited space and supplies on the journey to the red planet and the harsh conditions once there will force us to design systems that make the most of limited resources. In addition to scientific knowledge and development of new technologies, the perspectives we gain from exploring Mars may help us realize the interconnectedness of humanity and change the way we see our own planet. In going to Mars we won’t leave Earth behind; we will better equip ourselves to take care of challenges back home.

Mars Will Teach Us About Earth

Much of the water remaining on Mars is underground or frozen in glaciers. Although covered in dust, the composition of Martian glaciers may be quite like these earthly ones. Credit: NASA

We can better understand the processes that shaped early Earth through comparison with similar processes on other planets. Mars, the only planet we can put scientists on in the near future, holds well-preserved records of its past, making it a strong option for that second comparative data point. These records also detail its changes from an Earth-like planet several billion years ago, with liquid oceans and a thick atmosphere, to the frozen world it is today and can give us insights into paths that Earth may follow in the future.

Astronauts will be essential for complex scientific investigations like ice coring on Mars. As shown here, drilling ice cores in Greenland is a hands-on task. Credit: Reto Stöckli, NASA GSFC.

While robots will accompany them, humans are best suited to lead the next step in Martian science.  Investigations of records and global climate would benefit from the human ability to apply intuition and expertise to changing circumstances and handle complex machinery. For example, scientists could enable us to see a million- or billion-year record of Mars’ climate by collecting ice cores, long cylinders of ice that tell the history of the planet in their layers much like tree rings tell its age. The delicate processing of these ice cores makes their extraction a task best carried out in person. A human presence on another planet will allow us to better understand our first planet’s past, present, and future.

Mars Will Revolutionize Our Resourcefulness

Astronauts travelling in a Mars transit vehicle such as this one will have to be intentional about how they use, reuse, and recycle materials during the long journey. Credit: Boeing

In designing systems to operate far from Earth, we improve the technology to reduce our footprint on this planet. Transporting people and materials to Mars is expensive; it takes massive amounts of costly rocket fuel to get into space and to the Martian surface. This limits the mass of potential Mars transit vehicles and ensures they will be stocked only with critical items. During the months-long journey, astronauts must be intentional about their use of supplies onboard in order to make them last. This attention will continue on the Martian surface. Mars’ harsh, austere environment lacks many of the resources that humans rely on, and it will not naturally recycle those that we bring, as occurs with Earth’s water and carbon cycles. In Earth’s benign environment we can afford to discard materials like food, water, and plastics and to rely on non-renewable energy resources. Astronauts on Mars will not have that luxury.

Sometimes art imitates life. Energy on Mars could be delivered to astronauts through solar farms, similar those shown in “The Martian” movie. Credit: The Martian

While progress toward more sustainable living on our first planet is not contingent on a mission to Mars, the insights we gain could benefit the Earth. Travel to and life on our second planet present a unique design challenge – a harsh environment combined with financial, spatial, and material limitations – that requires the development of innovative technologies. New solutions intended for Mars can prompt the creation of technologies for Earth that propel us towards a sustainable, multi-planetary future. For example, we will refine life support systems, such as those that recycle urine into drinkable water and scrub the air of CO2 on the International Space Station; accelerate the development of alternative energy sources, with a focus on solar and nuclear; and invest in plastic reclamation technologies that would allow equipment and tools to be 3D printed from used plastics such as food packaging.

Mars Will Change Our Perspective

As seen from this CubeSat, the Earth and the Moon are barely visible. There will be a long stretch of time where our astronauts will see a similar view, with Mars slowly growing as Earth shrinks in the distance. Credit: NASA

Travel on Earth can open your mind to new ideas. Venturing out into deep space will be no different. Fifty-two years ago, the Apollo 8 crew became the first humans to see an earthrise ̶ our brilliant blue marble cresting over the barren lunar surface. There will be similar moments on our first human missions to Mars when, halfway between our two planets, both worlds are little more than colored specks outside the spacecraft’s windows. We can only imagine how the view from this previously unexplored area of space will affect our perspective. Floating in the black void will likely bring life’s fragility to the forefront of our minds. Perhaps we will rethink our Earth-based assumptions and our place in the solar system, but ultimately, we will only know the impact of that new perspective once humans experience it.

Taken on the first crewed lunar mission, this picture is a famous reminder of how small and fragile our planet really is. Credit: NASA

This isn’t a new idea; just as the earthrise inspired the astronauts who witnessed it firsthand, the images they took contributed to the environmental movement across America. Photos from the Apollo program sparked conversations around the care of “Spaceship Earth,” the imagery of our home serving as a reminder that it too is made up of interconnected systems with finite resources. Our efforts in space encouraged us to acknowledge our reliance on nature and each other and prompted us to act as better stewards of the Earth. A mission to Mars would likely amplify this effect.

Getting humans to that vantage point will bring about changes to the global mindset even before the first missions leave the Earth. It will take a global effort to realize a human Mars mission, through which we will learn how to share knowledge, organize multicultural working groups, and take advantage of every partner’s unique strengths. The lessons learned from collaborating on human missions to Mars will lay the groundwork for humanity to carry out other global efforts.

When we go to Mars, we will peer into the Earth’s past through Martian records and seek insights into our first planet’s future. The challenges of the mission will require creativity and ingenuity and will push us to develop technologies beneficial for both planets. We do not get a choice about efficient living on Mars, and we can adopt that same Martian grit to nurture Earth toward a better future. With humans on their way, we will gain a new perspective on our place in the solar system and on global collaboration, improving our ability to address other shared challenges at home. So, as we venture forth, we do so with our mind on both planets.

Human Missions to Mars: Lessons from COVID-19

By: Richard (Rick) Davis, Hannah Duke, Bob Collom

During this unprecedented and uncertain time, I find comfort in thinking about how our experiences on Earth translate into lessons we can apply to future Mars missions. Perhaps surprisingly, there are many ways in which the COVID-19 pandemic is preparing us for our journey to the Red Planet. Our experiences of isolation and adaptation to this new lifestyle are challenges that Mars astronauts must also master if they are to survive the first human mission to another planet. As we look toward pursuing a safer and healthier future, we can take note of lessons learned on how to sustain ourselves in our home world and apply them to the journey to our second planet. As you read this blog, feel free to tweet us @redplanetrick any lessons you’ve learned from COVID-19 that can apply to Mars missions. We will even update this blog as we get new ideas. Thank you!!

Where You Call Home

Our homes during this pandemic are our spaceships. They keep us safe from the dangers of the ongoing pandemic, just like the spacecraft that will protect Mars astronauts from the hazards of deep space travel. Despite keeping us safe, our homes can feel confining when we can’t go out to eat with friends or travel into work, school, or places like the gym. Astronauts on the International Space Station (ISS) can relate to what we’re going through, as they usually spend around six months confined to the station. Though the ISS is larger than a six-bedroom house, a lot of the habitable volume contains equipment and supplies, so space is limited. Mars astronauts will have a Mars Transfer Vehicle (MTV) to call home, and like most of us in our homes now, they will be confined to it for a long time. Specifically, the six to nine-month journey to the Red Planet, up to 500 days in the Martian system, and the six to nine-month return journey. So, it will be important for Mars astronauts to learn to manage living in a confined space for long periods just as we are now during the COVID-19 pandemic.

Astronaut Sunita Williams entering her sleep station on the ISS. Astronauts must zip themselves into a sleeping bag to prevent floating around in their sleep!

A big challenge for many during this pandemic is separating work life from home life. As we learn the best strategies for managing our time when stuck in the same place, we can maintain a healthier separation of work and rest. ISS astronauts, having been in similar situations to us now, share that they create boundaries on the station by sticking to a routine that allows them downtime, the ability to pace themselves in their work, and time for fun activities. Astronaut Scott Kelly admits that he misses the regimented routine on the ISS after returning to Earth. Mars explorers will need to use similar strategies to balance work and rest if they are to survive the long mission in a confined space.

Exercise can be a hard part of a routine to motivate – especially when sitting on the couch all day is an option. Astronauts embarking on deep space journeys probably won’t have a choice when it comes to exercise. ISS astronauts must exercise daily to mitigate the bone and muscle loss caused by living in microgravity. Since Mars astronauts will also need to keep their bones and muscles strong, they will likely exercise for around two hours a day like the ISS astronauts.

Astronaut Karen Nyberg running on a treadmill on the ISS to stay in shape while living in microgravity

The self-discipline it takes for us to maintain routines, exercise habits, and a healthy separation between work and home life during the coronavirus pandemic is no small feat. As we learn from one another about the best ways to deal with being quarantined in our homes, we can take the same lessons and incorporate them into our plans to send humans to Mars.

Your Fellow Crew

Astronauts on the International Space Station making the most of their limited space. Since there’s no up or down in zero-gravity, all surfaces can be used to “stand” on.

Just as some of us navigate living in quarantine with family/roommates around us, astronauts going to Mars will have to work closely with their crew members.  Even if you usually get along with your “crew” at home, extended quarantine can be frustrating, so communication is key to getting along. Similarly, since Mars crews will experience isolation with each other for a long time, interpersonal and communication skills will be essential. On top of this, since the crew will likely be international, it will be crucial for everyone to work well in a multi-cultural environment.

Within our own homes, we are experiencing how living with one person versus, say, five people makes for a different quarantine experience. For Mars missions, a larger crew brings more knowledge and problem-solving abilities, but it requires more space and supplies, whereas not having enough people on the missions could result in deeper feelings of isolation or even depression. Getting the right crew size is critical.

The Human Exploration Research Analog closed habitat at NASA’s Johnson Space Center.

To learn about optimal crew sizes and how crews operate in potentially hostile, isolated environments, NASA conducts analog missions such as the NASA Extreme Environment Mission Operations (NEEMO), the Human Exploration Research Analog (HERA), and Desert Research and Technology Studies (RATS). These missions help teach us how to better pick the astronauts that we will send together on the around 1100-day isolated mission to Mars. There’s also the UAE’s exciting Mars Science City Project that will provide a large-scale analog of a permanent human presence on the Red Planet.

An artist’s rendering of the UAE’s future Mars Science City near Dubai.

Even if you’re quarantining with a great “crew” during this pandemic, it’s still important to communicate with the friends and family you can’t see in person. We can apply what we’ve learned about staying connected during COVID-19 to help Mars astronauts also stay connected to family and friends back on Earth. The main difference is that since communication can only travel at the speed of light, Mars astronauts will experience some time delays in communications with Earth. Depending on the distance between Earth and Mars, the communication delay can reach up to 22 minutes one way, making it highly impractical for Mars astronauts to FaceTime with anyone millions of miles away on Earth. Thankfully, Mars astronauts will still be able to text, email, and send/view pre-recorded video messages.

Supplies & Suits

Most of us experienced great frustration when we went to the store and couldn’t find supplies like toilet paper, hand sanitizer, and other necessities. Then restaurants closed, limiting our food options. For Mars missions, food and supplies will be carefully planned out to last the around 1100-day mission, right down to what dessert options each astronaut prefers. Unfortunately, their food may lose flavor or even nutrients due to time or radiation exposure, so this will also require careful planning. Most of their food will likely be pre-packaged and stored in a way that minimizes volume, and since the cost of launching food and supplies is high, they won’t have the luxury of being wasteful. Having limited supplies is challenging and can be frustrating, but as we learned during the early months of this pandemic, careful rationing and planning helps us live with limited options.

Astronaut Chris Hadfield with some pre-packaged, dehydrated vegetables. A lot of food is sent dehydrated into space, so the astronauts must rehydrate it at a rehydration station before consumption.

Another adjustment to our lives is wearing a mask out in public. Mars astronauts will also need to adapt their wardrobe. When exploring the surface of Mars, astronauts will wear pressurized, temperature-controlled suits that provide oxygen and remove exhaled CO2. Going outside without one is not an option in the low-pressure, CO2-rich Martian atmosphere. The suits must also be dust-proof as it’s important to protect the astronauts’ lungs from inhaling Martian dust. From face masks to surface exploration suits, it’s critical to protect ourselves when venturing out into potentially hazardous environments.

On to Mars

Astronaut Tracy Caldwell Dyson on the ISS, looking out of the cupola window (Mars photoshopped to replace Earth).

There’s one last major commonality between our lives during COVID-19 and space exploration: both serve a greater purpose for humanity. Every day that we practice social distancing and stay home, we save lives. That thought makes it easier to tackle the challenges that come with living differently than we’re used to. Similarly, Mars explorers will take pride in knowing that they are progressing humanity’s knowledge and propelling us into a new age of space exploration.

So many brave medical workers are helping humanity by fighting COVID-19 on the front lines. Astronauts on the first mission to Mars will be on the front lines of space exploration, and it will take similar amounts of bravery to face such a feat. Though most of us aren’t on the front lines of COVID-19 or Mars exploration, we are still helping humanity achieve a healthier, smarter, and more adventurous future. Getting to Mars is a collective human effort, as is defeating COVID-19.

When astronauts embark on the long journey to Mars, know that you’ve already mastered some experiences similar to what they’ll live through. We’re preparing for a new era of adventure, and I hope you’re inspired by the thought that our experiences and skills gained during COVID-19 are not as far from the future of space exploration as they may seem. Consider viewing your new lifestyle and its obstacles as challenges to triumph. Take the mindset of a Mars astronaut and face this unprecedented time with courage and determination to problem-solve your way to the end. This is a difficult time for all of us, but together we will overcome this pandemic, just as together, we will get humans to Mars in the next era of space exploration.

Mars Recon Team Q&A with NASA Interns

By: Richard (Rick) Davis, Hannah Duke, Kallia Smith, Bob Collom

During a recent presentation to student interns at NASA, we received many questions. Although we were not able to answer all of them during the talk, we wanted to address as many as we could. Here are our answers to the first half of those questions. We welcome ideas and feedback. Great ideas can come from anywhere, and we want to encourage everyone to share their expertise and knowledge.

How do you join the mailing list?
You can join the mailing list by emailing

Mr. Collom or Mr. Davis, do either of you have LinkedIn or another way to stay in touch?
For more information about the Human Landing Sites Study, go to our website. We also have information about internships. You can also follow Rick on Twitter @RedPlanetRick. Let us know if you have any other questions!

I think Bob mentioned working in spaceflight policy. What is the average day working in spaceflight policy like?
 Spaceflight policy for getting humans to Mars is a relatively new area and projects are constantly evolving and growing, so a day in Mars spaceflight policy is anything but average. One moment you’re drafting a white paper that summarizes key topics for decision-makers, and the next moment, you’re organizing a meeting with space agencies from around the world. Other day-to-day tasks may include advocating for money to be spent on a specific project or searching for outreach opportunities that will reach young audiences. Spaceflight policy facilitates collaboration with subject matter experts across many areas who want to contribute to Mars exploration but are very busy, so you must be flexible, patient, and pleasantly tenacious. The ability to strategically plan, concisely communicate, curiously ask questions, and learn as you go are all important in this field. If you are willing to work hard, be bold in your pursuits, and understand that ‘we’ is a thousand times more powerful than ‘I’, Mars spaceflight policy can be a really cool way to contribute to the ever-dynamic world of Mars exploration.

Is that the spacesuit from The Martian (movie) on the first slide?
It’s an artist’s rendering of a potential suit for a future mission, but the visual design was inspired by The Martian. The suit from The Martian was based on discussions between NASA and the team behind The Martian about design considerations for a spacesuit.

An artist’s depiction of a Mars suit design.

So we never have had a spacecraft go to Mars AND return to Earth?
That is correct. All orbiters and landers so far have remained at Mars. However, our newest rover, Perseverance (launching this summer), will collect samples from the surface of Mars with the plan of returning them to Earth through the Mars Sample Return Campaign. This campaign will be a key step in getting humans to Mars as it will be the first-ever round trip to Mars and back, including the first launch from the surface of Mars.

Has the time it takes to send rovers to Mars decreased over the years
Based on the most efficient orbital trajectory, the time to travel to Mars is between 6-9 months, and all the rovers sent so far have had an average of an eight-month-long trip. Windows of time for launching to Mars are based on the locations of Earth and Mars relative to each other as they go about their orbits. The launch window for the most efficient trajectory opens every 26 months.

What are your plans to reduce the cost of these missions so that astronauts and billionaires aren’t the only people on Mars?
Increased innovation and partnerships are key for reducing the cost of missions. When innovation is aimed at getting us to Mars more efficiently, it can lead to new methods and techniques that save a lot of money. Innovation is occurring across many areas such as entry, descent, and landing systems, small nuclear reactor designs, and supersonic retropropulsion techniques. Partnerships are also key for lowering costs and enabling innovation. For example, NASA’s Commercial Crew & Cargo Program has invested significantly in the private sector to develop more efficient and cost-effective space transportation methods. The Artemis program (the first step towards maintaining human presence in deep space) is leveraging similar partnerships with American companies who will deliver payloads to the moon through the Commercial Lunar Payload Service (CLPS). We anticipate that similar partnerships will help cultivate a more cost-effective exploration of Mars.

Is Mars covered under the Outer Space Treaty? As more countries travel to Mars, how do you enforce that everyone follows the same rules to avoid international conflict on Mars?
Mars is covered under the Outer Space Treaty, which states that space is free for all countries to explore for the benefit of humanity, is currently the guiding principle for government in space. However, the treaty does not implement specific laws or a governing body to enforce them. As more countries move into space and as more people begin to live in space, we don’t yet know how the treaty will evolve to cover the specifics of everyday life on the moon or Mars.

How do you think private companies such as SpaceX will impact our trip to Mars?
Going to Mars is a collective human effort, so we are going to need a lot of institutions, both private and international, to work together. This will bring in new ideas and allow for more efficient production and cost sharing.

What technologies of the lunar Artemis missions do you see translating over for future Martian missions?
Lunar missions can teach us many lessons in preparation for Mars. The principal mission components, such as habitat, rover, and power system designs, will likely be similar in both environments. For example, the Mars Ascent Vehicle could be modeled off the vehicle launching from the moon. In addition, lunar suits will need to be lightweight (gravity on the moon is 1/6 that of Earth’s, while gravity on Mars is 1/3), easy to maintain, protect from dust, and have high mobility which are all things Mars suits will need. However, there are also critical differences between operating on the moon and operating on Mars. For example, Mars has an atmosphere (albeit very thin), whereas the moon does not, so entry, descent, and landing (EDL) systems used for a lunar landing will not necessarily apply to Mars. Since the moon has no atmosphere and can have up to two-week nights, equipment will stay very cold for long periods of time. In contrast, Mars has a more Earth-like day (averaging 24 hours and 39.5 minutes), so equipment won’t have to face such long durations of extremely low temperatures.

How long are people going to spend “living” on Mars?
Missions to Mars will include a 6-9 month trip there, 500 days in the Martian system (either in orbit or on the surface), and a 6-9 month journey back. Looking at the history of exploration, such as McMurdo Station in Antarctica, the ISS (see pictures below), and Mars rovers, we generally take a step-by-step approach as we build up to more capability. For example, initial rover missions to Mars were very small (see picture below), but now we can send rovers weighing about a metric ton to the surface. If we assume that this approach applies for human missions to Mars, it suggests that initial surface missions will likely be short stays, with the majority of the astronauts’ time spent in orbit. As we gain more experience on the surface of our second planet, we would expect the time on the surface to greatly increase.

ISS progression from early stages to today. Credit: NASA
Comparison of Mars rover sizes over time. Credit: NASA

When thinking about the people who will go to Mars, do you think a crew will be made up of people from strictly STEM fields, or that there will be a need to think more expansively about who should go, especially with a much longer timeline?
Initially, a Mars crew will include highly technical people. We anticipate that some of the disciplines needed will probably include, doctors, engineers, pilots, and other scientists such as astrobiologists. We may even need artificial intelligence experts to operate the computers. We also expect astronauts to cross-train when needed. For example, a pilot might train as a backup doctor in case the doctor gets sick. In addition, we fully anticipate that these missions will be international missions, so the crew must work well in a multi-cultural, remote, high-stress environment. As we continue to develop a more sustained presence on the surface of Mars, the occupations needed will likely expand, reflecting more of the diversity of occupations found on Earth. 

What are the objectives/tasks of the astronauts once they land on Mars? Has that part of the plan been discussed yet?
As we stand on the surface of another planet for the first time, there will be many exciting and fascinating science objectives waiting to be explored by Mars astronauts. For example, there is a chance that life could exist on Mars, and explorers will have the opportunity to conduct astrobiology studies with more expertise and depth than ever before, possibly uncovering the first evidence of past or present life outside Earth. In addition to astrobiology studies, there will be many other high priority science objectives likely including in-depth studies of the geology, climate, atmosphere, and human research, to name a few. NASA has had several studies to help determine which activities would benefit most from having a human present (rather than robots or rovers) on the surface of our second planet. Humans will bring more creativity, adaptivity, and responsiveness to the Martian environment, enabling a more advanced process of discovery.
In addition to conducting major science activities, we expect that the astronauts will check out and assemble equipment and modules that landed prior to the crew’s arrival. Some of this assembly will aim to create a sustained presence on the Red Planet. This human activation and assembly approach worked very well on the ISS, and we expect that it will work well on Mars too.

Will astronauts on Mars be growing and eating their own food or primarily relying on supplies? In regard to renewable agricultural systems on Mars, what are some ideas that have been proposed?
 For initial missions, we will likely send pre-packaged food with the crew. However, there are challenges associated with preserving taste and nutritional value in food that has been stored for long periods. If we can figure out how to grow food efficiently on Mars, we can fix the issues concerning taste and nutritional value while also reducing the total mass transported from Earth. Agriculture on Earth requires large amounts of dirt and water, which would be very heavy to carry into space, so astronauts would need to utilize efficient agricultural systems and local resources to grow their food. Since the regolith on Mars does not contain organic material, one option is to use hydroponics, where a plant grows in a nutrient-rich solution that doesn’t require dirt. It might also be possible to grow plants using minerals found in the Martian regolith, but toxins such as perchlorates would have to be removed. Despite the challenges, implementing an efficient agricultural system on Mars would reduce the mass and cost of missions while likely increasing morale for the astronauts.

Would astronauts have separate suits for space travel as well as Mars surface or is it one suit that handles both conditions?
 Mars astronauts will need a different suit for surface exploration than the spacesuits they will use in zero-gravity to perform spacewalks or exterior repairs to the Mars Transit Vehicle. In general, surface suits will have to be lighter, easier to maintain, and will have to withstand elements like dust better than current spacesuits. ISS spacesuits weigh about 275 pounds on Earth, but since they are worn in zero-gravity, the weight is less important. (The mass of the suit, however, is still an essential consideration due to inertia. Once you start moving, it’s a lot more challenging to slow down or stop since there’s no gravity or friction.) However, in Martian gravity (about 38% of Earth’s), astronauts will feel the weight of their suits, so Mars surface suits will have to be much lighter while also maximizing mobility. In addition to being lighter, Mars surface suits will also have to be easier to maintain than current spacesuits. It won’t be ideal to have suits that require a lot of maintenance or prep before excursion like the ones on the ISS. Another challenge for surface suits is the need to keep dust out. On the moon, the regolith has not been weathered, so during Apollo missions, it acted like shards of glass, slicing astronauts’ suits when they moved their arms. On Mars, we expect the regolith to be more weathered than the moon, but this is still a concern for suit integrity. Also, if there is any life on Mars, it could be transported through the dust, which is another reason to have dust-proof surface suits.

Do we need to bring water from Earth? If so, how do you bring so much water to Mars?
 Water is heavy, which presents a challenge when bringing it from Earth. However, the presence of water feedstocks (sources) on Mars offers many opportunities to extract and use water for various demands. Water on Mars comes in several forms, such as subsurface ice (major ice deposits just below the surface of Mars) and hydrated minerals (water molecules contained within minerals), both of which could be harvested for use by humans on Mars. Bringing some water will be necessary for the trip from Earth to Mars. However, we want to maximize the amount of water we can get from Mars by carefully choosing a landing site conducive to in-situ resource utilization (ISRU). For initial missions, the most extensive water demand will likely be propellant for the Mars Ascent Vehicle (MAV).

What do you think about settling on the moons of Mars rather than the planet, to avoid the gravity well?
Mars’s moons, Phobos and Deimos, are very low gravity bodies, to the extent that landing on them is more like docking in space. This will probably make them well-suited for short visits, but less so for extended settlement, since it’s more difficult for humans to live and work in microgravity, as on Phobos or Deimos, than in partial gravity, as on Mars. Initial missions to Mars could very likely be orbital missions as we work our way up to landing missions, and some of these orbital missions could include sorties to land on Phobos and Deimos.

The Martian moon Phobos (moving white dot) orbits Mars, as seen from the Hubble Space Telescope

Could you explain how we are going to have breathable air on Mars?
95% of the Martian atmosphere is carbon dioxide, which can be broken down into oxygen and carbon monoxide. The oxygen can then be used to produce breathable air. The Mars Oxygen In-Situ Resource Utilization Experiment(MOXIE), an instrument on the Perseverance rover, will test the technology necessary for this process.

Are we still considering something like the dome-like structures tested at HI-SEAS?
Initial missions to Mars will likely use smaller pre-built modules, because smaller modules are easier to transport and land on Mars. Domes may also require local construction, instead of being prefabricated on Earth, which would be very challenging on the Martian surface. Future, longer-term missions may use a dome-like design because they provide a larger volume for the crew to live in. If these domes are clear, they could even simulate the feeling of being “outside” without a Mars suit on.

The dome-like habitat used in the HI-SEAS analog mission in Mauna Loa, Hawai’i. Credit: Sian

Do you think that the protection afforded by underground structures to dust storms are worth not having windows?
 We do not generally anticipate that dust storms would be a reason to design habitats without windows. Due to the low density of the air, the force exerted by wind would be low, and therefore would not affect the integrity of the windows.
Reducing the crew’s total radiation exposure may be a reason to consider underground structures. In that case, a combination of aboveground and underground structures may be ideal. Astronauts could sleep underground to reduce their total radiation exposure, while living areas aboveground could allow astronauts to monitor/operate activities outside. Aboveground structures also promote the psychological benefits of seeing the surrounding environment and sunlight. For an idea of what these structures on Mars might look like, check out this fascinating TED Talk by Bjarke Ingels.
Having such windows has been incredibly helpful on the ISS (pictured below) because it provides astronauts a way to oversee/monitor spacewalks and robotic arm activities as well as conduct Earth observations.

How do you test radiation protection ideas on Earth? Is there a test facility? How far from Earth do you need to go for a representative environment?
 NASA has several facilities that test whether electronics and other instruments on a spacecraft can withstand deep space radiation (you can read more about one of these types of centers here). A lot of the protection measures we hope to implement will integrate radiation-shielding materials into spacecraft and surface structure (habs, labs, etc.) designs. Since we have flown dosimeters out into deep space, we have a good idea of how much radiation humans would experience from both solar radiation and galactic cosmic radiation (GCR). A representative environment of deep space radiation occurs outside the Earth’s magnetosphere (pictured below), which traps energetic charged atomic particles in areas called the Van Allen Belts, protecting Earth’s atmosphere from receiving high amounts of radiation.

Cross section of the Van Allen Belts compared to Low-Earth Orbit and Geosynchronous Orbit. Credit: NASA

How effective is electric propulsion on the surface of Mars?
 We won’t use electric propulsion on the surface of Mars. Rovers will use either electricity stored in fuel cells or batteries or generate their own electricity through solar panels or radioisotope thermal generators (RTGs). Curiosity and Perseverance both make use of RTGs, which uses the decay of plutonium to create heat and electricity. You can read more about the use of this power supply on Perseverance here. On the cold surface of Mars, power will be critical, and the most likely sources of electricity will be solar panels, RTGs (possibly on the rover), and small nuclear fission reactors. Rovers will need to be able to store this energy which can be done using fuel cells or batteries.

Are there any other plans to produce energy on Mars, that are sustainable, other than solar panels?
 Solar power alone will probably not meet the full energy needs of a human mission to Mars. Dust storms on Mars could block out sunlight, making the atmosphere opaque enough that there is not enough light reaching the solar panels to generate power. A human crew may also land at a mid-latitude location on Mars, where days are much shorter than nights in winter, again providing less sunlight. To deal with these challenges, NASA is currently working to develop compact nuclear reactors that will not be dependent on solar energy. Unfortunately, other sustainable energy options such as wind and geothermal energy are not viable options for renewable energy on Mars. The winds are less powerful due to the extremely low density of the Martian atmosphere, and we have not yet found evidence of widespread geothermal activity.

Is the reason to keep the lander and Mars Ascent Vehicle as separate vehicles to leverage ISRU for fueling the Mars Ascent Vehicle (rather than carrying all the necessary fuel)?
 To make Mars missions more affordable, we will need to learn to use local resources to reduce the overall mass transported from Earth. One of the biggest ways to do this would be to use Mars resources to create the fuel and oxidizer necessary for the Mars Ascent Vehicle (MAV). We will take advantage of the CO2 rich atmosphere by extracting the oxygen for use as our oxidizer. For the first missions, we plan to take methane for the fuel with us, but over time, we can utilize water (H2O) sources on Mars to produce the hydrogen needed for methane (CH4) with the carbon coming from the atmosphere. Using ISRU to create fuel and oxidizer for the MAV would drastically reduce the amount of mass transported from Earth. This, in turn, greatly reduces the overall cost of Mars missions.

How much thrust or ISP will you need to get off the surface of Mars?
 The amount of thrust needed to get off the surface of Mars will depend on the mass of the Mars Ascent Vehicle (MAV). A lot of work is being done to minimize the mass of the MAV. Thrust and specific impulse (Isp) are separate concepts, but both are important components to launching the MAV. Thrust is the force generated by the propulsion system. Specific impulse (Isp) defines the efficiency of the propulsion system and depends on the type of propellant used. To reduce the cost of Mars missions, we are looking at using local resources on Mars such as methane and oxygen for the MAV propellants. Both can be produced locally and stored easily. Since local resources will drive our choice of propellants, they will also drive what the specific impulse to get off the surface will be.

I’ve seen that SpaceX is developing their Raptor engine that runs off methane instead of the typical liquid oxygen (LOX) mixture; is NASA developing a similar style engine to use on Mars? I believe they chose methane in hopes of being able to develop more fuel in-situ.
 Yes, NASA is currently planning to develop a methane engine. Most Mars mission architectures generally assume that a methane engine will be used because methane (CH4) can be made locally by combining carbon from the atmosphere and hydrogen from water. Oxygen, which must be combined with the fuel (in this case, methane) for the engine to ignite, can also be made locally using carbon dioxide in the atmosphere of Mars. In addition, methane is easy to store for long periods of time.

Is artificial gravity not currently viable for the MTV? What are the largest constraints?
 Artificial gravity is a possibility for future missions, but initial human missions will probably not require it. As seen with astronauts on the ISS, consistent exercise helps counteract the bone and muscle loss that occurs from living in zero-gravity. It also appears that the bone and muscle loss levels out over time spent in space. However, we should be mindful that ISS missions are usually about 180 days whereas Mars missions will be about 1100 days, so we would be extrapolating our knowledge. We believe that we can manage these effects of zero-gravity through exercise for longer missions, but we need more data from astronauts who have spent more time in space to be sure. If we find we cannot manage zero-gravity effects with exercise for Mars missions, we may then consider other solutions such as artificial gravity for the Mars Transfer Vehicle.
We could generate artificial gravity by rotating a section of the spacecraft, simulating the feel of gravity through centrifugal force. However, there are many challenges that come with this. If the rotating arm is too short, astronauts may experience dizziness anytime they turn their heads away from the plane of motion. In contrast, making the arm longer would pose a significant engineering challenge since building and launching a more massive spacecraft would be more difficult and expensive.
When planning our first missions to Mars, we must carefully consider which technologies are mission-essential. As we have found in previous programs (such as the International Space Station), we can anticipate some risks, but there are other risks that we will only learn of as we start to plan, train, and execute missions in that program. We need to keep the Mars Transfer Vehicle as simple as safely possible so that we can get to Mars sooner rather than later and learn about these other risks. These risks, particularly on an 1100-day mission, could also be a danger to the crew, so we need to understand them so that we can manage them along with the risks we are currently aware of.

The fictional Hermes spacecraft from the movie The Martian based on the novel by Andy Weir. Credit: Scott Free Productions

How do you think ion engines will fit into longer distance space travel? Although they offer slower accelerations, they do offer longer “burn” times and can eventually reach the same velocities as liquid chemical engines?
 Ion engines, or electric propulsion in general, will likely be a key part of enabling travel to Mars because this type of engine reduces the amount of propellant needed to reach Mars. However, they are slower to accelerate. For transporting cargo, travel time doesn’t matter as much, making electric propulsion a slow but cost-effective option, much like we use slow-moving barges to transport cargo on Earth. For human crews, the best solution may be a hybrid that includes a high-thrust chemical engine and efficient electric propulsion.

How far has exercise science been developed for extended time on Mars?
 The exercise regimen for astronauts on Mars will likely resemble the regimen for astronauts on the ISS. Since Mars has one-third the gravity of Earth, the effects on the body will likely be less extreme than ISS astronauts experience in zero-gravity. Regardless, astronauts will still need to exercise to ensure that they will be in good shape throughout the journey. Portions of the mission will require the astronauts to be physically strong, such as landing and ascent from Mars, exploring the surface, and withstanding the g-forces during Earth reentry.
Astronauts on the ISS use equipment modified for exercise in microgravity. Each piece of equipment focuses on either aerobic or anaerobic exercises. An example of anaerobic exercise equipment includes the ARED (Advanced Resistive Exercise Device), which uses vacuum cylinders to simulate free weights for strength training that prevents muscle atrophy.

ARED on the ISS. Credit: NASA

For aerobic exercise, there is the TVIS (Treadmill with Vibration Isolation and Stabilization). This treadmill uses bungee cords to hold the astronaut in place.

On the ISS, astronauts run while secured to TVIS with bungee cords. Credit: NASA

Astronauts can also use the CEVIS (Cycle Ergometer with Vibration Isolation System) for aerobic exercise. It’s similar to a stationary bike on Earth, but it’s bolted to the floor of the ISS, and astronauts must wear a seat belt to stay in place while working out.

CEVIS on the ISS. Credit: NASA

Engineers are currently designing smaller versions of these machines so that missions to Mars, which might use a vehicle smaller than the ISS, can be as efficient with their mass and volume as possible.

Is there any development on drugs/enhancements to help with the health issues associated with long term zero-gravity space travel?
 At this time, we do not expect to need pharmaceuticals to manage the health issues associated with long-term zero-gravity space travel. By studying astronauts on the ISS who experience zero-gravity for long periods, we have found that regular exercise greatly mitigates harmful side-effects such as bone deterioration and muscle atrophy. We have also seen that over the average six-month stay on the ISS,  bone and muscle loss levels out, but more hard data is probably needed to determine whether this will be applicable to longer missions like a 1100-day Mars mission.

Can you speak to the capabilities of Curiosity’s on-board lab?
 Curiosity, which holds the Mars Science Laboratory (MSL), is the most scientifically advanced rover we’ve landed on Mars to date. Over the last eight years, Curiosity has characterized the mineralogy, geology, and chemistry of the Martian surface in Gale Crater. Examples of some of the things it can do include identifying the chemical composition of rocks and soil, searching for organic compounds, and reporting on the meteorological conditions around the rover. You can read more detail about the MSL here. Perseverance (our rover launching this summer) will build upon Curiosity’s achievements by taking  one step further and collecting rock and soil samples for planned return to Earth as part of the Mars Sample Return Campaign.

A panorama of Teal Ridge in Gale Crater taken by Curiosity.

Can you comment on how MEDLI2 will help these future missions?
 The Mars Science Laboratory Energy Descent and Landing Instrument (MEDLI) is the set of sensors currently on Curiosity. This interview with Michelle Munk, the subsystem lead for MEDLI, goes into more detail. MEDLI2 is a second set of sensors on Perseverance. When Perseverance lands on Mars, MEDLI2 will collect data about its descent and the Martian atmosphere, which will give us information about how to best land a human crew on Mars, such as how to deal with the extreme heat generated during landing.

What will happen to the ISS after it reaches its end of lifetime?
 The International Space Station’s estimated operational lifetime extends through 2028. At that point, all the countries involved, including the US, will need to decide whether certain modules should be retired or replaced (not all modules on the ISS have the same end date, since they were not all launched at the same time). Options for the ISS include letting it deorbit, replacing old modules, allowing private companies to take over its operation, or letting it continue as normal. This article from the Planetary Society goes into more detail about these options. We’re finding out that operating in the vacuum and zero-gravity environment of space is not as hard on machines as we expected, since the ISS modules are lasting longer and with less maintenance than originally anticipated. Overall, we are learning more about the ISS as we go: the lifetime of the ISS has been extended before, and it might be extended again.

Why are the solar panels all of different angles if the sun is in the same location?
 Solar panels on Earth and on spacecraft are angled to maximize solar exposure, and we will want to do the same thing on Mars if we decide to use solar power there. Some solar panels on Earth can also rotate to follow the path of the sun throughout the day.
In general, solar arrays would all point in the same direction to maximize the impingement of sunlight on the solar panels. It’s not clear from the picture whether there’s distortion based on the angle the photo was taken at, but in general, we would expect the solar panels on the ISS to face the same direction.

The International Space Station. Credit: NASA

Mars Rover Perseverance: A Key Step Toward Human Exploration of Mars


By: Richard (Rick) Davis, Bob Collom, David McIntosh, & Michelle Viotti 

Artist Concept: Mars rover Perseverance sets out to seek signs of life – and prepare for a human future on Mars. Credit: NASA/JPL-Caltech

Exciting times as Mars 2020 Rover Perseverance is getting ready to set off on a life-seeking mission, but it marks the beginning of so much more! The Mars 2020 mission is actually the first of a multi-mission effort to return samples from Mars to Earth. That interplanetary round-trip campaign is a precursor for future round-trip crew-carrying spacecraft that will take humans back and forth between Earth and Mars over several missions, ultimately leading to a sustained human presence on the surface of the red planet!

The returned samples that Perseverance collects will be critical for high-priority scientific investigations about microbial life, but will also allow human-mission planners to understand the mechanical properties of the Martian dust, dirt, rocks, and minerals (the “regolith”) – that is, how abrasive they are, their oxidizing potential, particle size and shape, etc. That information will teach us about potential human-health hazards: toxicity, respiratory issues, and potential biohazards of any existing microbial life on Mars etc. These data will help mission planners design strategies to safeguard Mars explorers. The analysis of minerals in the returned samples may also have a direct impact on understanding what natural mineral resources are potentially available for future human use on Mars.

Beyond kicking off the Mars sample return campaign, Perseverance will gather mission-enabling knowledge critical to every phase of humanity’s own future round-trip voyages to Mars: getting safely to the Martian surface, living and working on Mars, and returning home to Earth.

Getting Safely to the Martian Surface

The Mars Entry, Descent, and Landing Instrument (MEDLI) will tell mission planners how to protect humans during entry, descent, and landing, one of the riskiest parts of any Mars mission. Credit: NASA/JPL-Caltech

The Mars 2020 aeroshell that protects the rover on its journey carries sensors that will tell us how the spacecraft heats up and performs during entry into the Martian atmosphere. That information will help engineers improve landing designs for the larger crew and cargo landers necessary for human missions. During descent, the rover will demonstrate a new autonomous guidance system called Terrain Relative Navigation (TRN). This hazard-avoidance system may join beacons and other technologies that support landing large cargo in advance of humans, as well as eventual piloted landings by crewed vehicles.

Living and Working on Mars

Right: Artist concept of a possible in-situ resource utilization (ISRU) facility (foreground) on Mars. Credit: NASA

Mars is an extreme environment, but Perseverance is going to make the most of it. The rover carries a special “lung” that will produce oxygen from Mars’ carbon-dioxide atmosphere. It will be the very first demonstration of how to process natural resources on Mars for human use. Large quantities of oxygen will be needed to produce propellant (“rocket fuel”) for astronauts’ return trip home to Earth, as well as to provide back-up oxygen supplies for breathable air.

The oxygen-generating instrument will also monitor how abundant Martian dust in the atmosphere interacts with machinery to improve future engineering designs. In addition, Perseverance’s new weather-monitoring capabilities are specially designed to enhance our understanding of the relationship between dust and weather through the Martian seasons. Learning more about Martian dust will help engineers design better shelters for astronauts, as well as equipment that has to function for long durations on the surface. After all, Mars-bound explorers will want to know their equipment will work for years in the Martian environment.

Once at home on the surface, future human explorers venturing outdoors on Marswalks will need spacesuits that are strong enough to withstand the elements, but flexible enough to move around with agility. Perseverance carries five samples of different space-suit materials to see how each performs in long exposures to radiation and dust in the Martian environment.

As they explore, robotic companions will likely join the crew to enhance their scientific investigations and help keep them safe, just as Perseverance has a helicopter pal named Ingenuity. Like drones here on Earth, Ingenuity will soar overhead, demonstrating how future aerial vehicles could scout out compelling places for humans to explore – or venture into places too steep or too hazardous for people.

Perseverance carries a ground-penetrating radar called RIMFAX (Radar Imager for Mars’ subsurface experiment), which will reveal the Martian subsurface. Artist Concept. Credit: NASA/JPL-Caltech/FFI

Perseverance also demonstrates the first ground-penetrating radar on the Martian surface. Similar systems will land at a potential human base in advance of people arriving, to look for precious water resources found in subsurface water ice. Just as we can extract valuable resources from the Martian atmosphere, water ice on Mars can be processed to produce hydrogen, another key ingredient of propellant needed for launching back to Earth from Mars.

While Perseverance’s landing site in Jezero Crater is likely too close to the equator for water ice to be present, a future ice-seeking orbiter will be able to calibrate its radar with Perseverance’s results, helping to ensure resources are really there and accessible before humans arrive. Seeing the structure of subsurface rock layers will also ensure that the ground below is stable enough for landing heavy human-class payloads such as a life-supporting habitat and for building a launch pad and other infrastructure needed by human explorers.

Returning to our Home World: Earth

The “Mother Ship” (Mars Transfer Vehicle) will transport humans back and forth between Earth and Mars. Credit: NASA

Thanks to the Mars 2020 mission, living and working on Mars will be safer and more comfortable, from habitat design to “walkabouts.” When the first humans are ready to blast off from Mars on their voyage back to Earth, they will use oxygen, hydrogen, and methane fuel that can be traced back to Perseverance’s demonstrations of how to use Martian natural resources. And, just like the samples Perseverance collects, Mars astronauts will launch on a Mars Ascent Vehicle and reunite with a “Mothership” that will carry them safely home. While sending humans to Mars is a complex endeavor, making step-by-step progress through Perseverance and other advances, our human adventure on Mars is closer than ever.

Looks Can Be Deceiving

By Richard (Rick) Davis and Bob Collom

It’s funny, actually. The above panorama, courtesy of the Curiosity Rover, makes Mars look like a desert in Arizona, somewhere hot and rocky but habitable. But, Mars isn’t like any desert in Arizona. Mars has more in common with the summit of K21. It might look sunny, but the temperature sits around 32°F at midday and gets down to -110°F at night2. There is an atmosphere, but it’s impossible to breathe due to the fact that it’s 96% Carbon Dioxide with only 1% the density of the atmosphere on Earth. By comparison even the top of K2 averages 19°F during the day and 0°F at night and still has 33% of the atmospheric density as compared to sea level.

We will learn to master this terrain. But, these panoramas can trick us; they can make it look like the surface of Mars is safer than being in space. In truth, however, humans have been living in space for decades, and have learned how to do so safely. We have never tried to live on another planet. If there was a rule for Low Earth orbit missions it would be, “space is dangerous; the surface is safe.” We need to be careful not to get stuck in a paradigm and assume the same rule applies to Mars. We need to look at this panorama and see past the beautiful, Earth-like landscapes, to the challenges that underlie them. Mars is nowhere near as safe as the amazing planet that we call home!

These misconceptions are exciting for me. They point to all of the mysteries that still need to be uncovered and all of the technology we need to develop. We will need to practice and learn before we know as much about living on Mars as we do living in space. It strongly suggests that we will need to incrementally step our way to permanent presence on Mars—with orbital missions coming first, followed by short and then increasingly longer stays on this new planet. Even this step wise approach will be incredibly challenging as we learn to overcome the challenges that Mars poses, but if becoming a multi-planetary species was easy, it wouldn’t be fun!

[1] The second tallest mountain on planet Earth and the hardest mountain to climb
[2] Based on air temperature data from the Curiosity rover in Gale crater taken over the course of 200 sols

Mars is Closer Than You Think

By Richard (Rick) Davis and Bob Collom

What qualifies as a challenge for a society evolves as the society evolves. The frontier has moved beyond the west, beyond the surface of the Earth, and beyond the Moon. Our frontier is at Mars. What took Roald Amundsen a lifetime of effort can be replicated in a matter of days now. What took Lewis and Clark more than 2 years can be accomplished in a matter of hours. These things are easy today, they are not a challenge, and they do not inspire. It will not be easy to traverse the expanse of space and land on an entirely new planet, but exploration is not about doing what is easy.

On May 25, 1961, when Kennedy first said, “I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth,” humanity was only taking its first steps into the frontier of space. Only two people had left the Earth for a cumulative time in space of just over two hours, and yet Kennedy and a nascent NASA proclaimed that America could put an astronaut on the Moon. Fast-forward to today, humanity has spent more than 50,000 days in space, launched thousands of rockets and hundreds of astronauts, developed supercomputers millions of times more powerful than those of 1961, and visited every major body in our solar system. Mars may be 200 times farther than the Moon at closest approach, but we may be thousands of times more prepared to achieve this.

Mars is a destination that compels and inspires. To quote a recent college student and an aspiring Mars explorer, “The first person to walk on the moon didn’t happen in my life time but I would love to be a part of the first humans on Mars.” This energy will propel humanity beyond the confines of the Earth and out into the Solar System. From the Mercury Program to the Curiosity rover, we have been preparing to send humans to Mars for 60 years.

The following table underscores how much our capabilities have grown since 1961:

The following tables outline more detailed areas of comparison:


[1] The date of JFK’s speech before a joint session of Congress in which he committed the nation to landing a person on the Moon
[2] Includes Yuri Gagarin and Alan Shepard’s flights
[3] Compiled from astronaut, cosmonaut, taikonaut, and space tourist biographies
[4] Alan Shepard’s May 5, 1961 Mercury-Redstone 3 flight
[5] Achieved by Pioneer V on June 26, 1960
[6] Achieved by Voyager 1 as of August 4, 2017
[7] From the historians at the Museum of Computer History
[8] Floating Point Operations Per Second
[9] Includes Vanguard 1, Vanguard 2, Explorer 7, Transit 2A, Solrad 1, Echo 1, Explorer 9, Discoverer 20, Discoverer 21, Discoverer 23, and Explorer 11
[10] Includes active solar system probes. Taken from:
[11] Includes Russian, US, and Chinese crewed launches
[12] Includes ESA member nations
[13] Starting on Oct. 31 2000 with ISS expedition 1
[14] Average perigee for Moon and Mars from: and the calculations of Ryan Woolley
[15] His journey from Ft Niagara to the mouth of the Mississippi that claimed much of what became the Louisiana Purchase
[16] Crew Perished on return journey
[17] Adjusted for inflation to 2016 dollars
[18] Adjusted for inflation to 2016 dollars

Frontiers Shatter Complacency

By Richard (Rick) Davis and Max Parks
The Martian moon Phobos (moving white dot) orbits Mars, as seen from the Hubble Space Telescope

My name is Rick Davis- I work at NASA Headquarters, where I work in the Mars Exploration Program and co-lead the effort to choose the landing site for humans on Mars. In my time at NASA, I’ve instructed Space Shuttle crews, was a Space Station Capsule Communicator, and worked in Russia for three and a half years, coordinating NASA’s presence at Star City– the home of Russia’s Cosmonaut Corps.

My life as an engineer is only part of the picture. Before I studied aerospace engineering, I studied history. As I learned about the past, the idea of frontiers, and how important they are to us as a species, became central to my perspective of the universe. That’s why I’m so passionate about Mars.

La Salle on the Mississippi

Pushing into a frontier is important. Human beings thrive when success is not guaranteed. Frontiers are like that for entire societies. Voyages of exploration like that of Lewis and Clark, or the French explorer La Salle, the first European to sail the length of the Mississippi River, bring out the bravest and most ingenious within us. Rising to meet the challenges that we face on a frontier helps us learn more about ourselves and about our place in the cosmos. Without the risks of exploration, unless we challenge the unknown, complacency will prevent humanity from achieving our full potential.

Mars is the next step in exploration, and when I see the amazing work being done by the people at NASA, in industry and in academia, as well as in so many other national space programs, I know that we’re ready for this step.

Sunrise on Mars

To be frank, I was unsure about starting a blog. But Mars is challenging- to do it right, we will need a lot of ideas. Hopefully, by sharing stories as more is learned about Mars, this blog can help spark new ideas. The fact is, we don’t yet know if we can live on an alien planet; there are tremendous challenges we are working to solve. If you have ideas, we want to hear about them. We need ideas from all over to make this happen.


To follow the effort to select a site for the first human base on Mars, head on over to
To contact us, send an email to