No Phosphine on Venus, According to SOFIA

by Anashe Bandari

Venus is considered Earth’s twin in many ways, but, thanks to the Stratospheric Observatory for Infrared Astronomy (SOFIA), one difference now seems clearer: Unlike Earth, Venus does not have any obvious phosphine.

The planet Venus with a spectra laid over it
The spectral data from SOFIA overlain atop this image of Venus from NASA’s Mariner 10 spacecraft is what the researchers observed in their study, showing the intensity of light from Venus at different wavelengths. If a significant amount of phosphine were present in Venus’s atmosphere, there would be dips in the graph at the four locations labeled “PH3,” similar to but less pronounced than those seen on the two ends. Credit: Venus: NASA/JPL-Caltech; Spectra: Cordiner et al.

Phosphine is a gas found in Earth’s atmosphere, but the announcement of phosphine discovered above Venus’s clouds made headlines in 2020. The reason was its potential as a biomarker. In other words, phosphine could be an indicator of life. Though common in the atmospheres of gas planets like Jupiter and Saturn, phosphine on Earth is associated with biology. Here, it’s formed by decaying organic matter in bogs, swamps, and marshes.

“Phosphine is a relatively simple chemical compound — it’s just a phosphorus atom with three hydrogens — so you would think that would be fairly easy to produce. But on Venus, it’s not obvious how it could be made,” said Martin Cordiner, a researcher in astrochemistry and planetary science at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

There may be other potential ways to form phosphine on a rocky planet, like through lightning or volcanic activity, but none of these apply if there simply isn’t any phosphine on Venus. And according to SOFIA, there isn’t.

Following the 2020 study, a number of different telescopes conducted follow-up observations to confirm or refute the finding. Cordiner and his team followed suit, using SOFIA in their search.

The recently retired SOFIA was a telescope on an airplane and, over the course of three flights in November 2021, it looked for hints of phosphine in Venus’s sky. Thanks to its operation from Earth’s sky, SOFIA could perform observations not accessible from ground-based observatories. Its high spectral resolution also enabled it to be sensitive to phosphine at high altitudes in Venus’s atmosphere, about 45 to 70 miles (about 75 to 110 kilometers) above the ground — the same region as the original finding — with spatial coverage across Venus’s entire disk.

The researchers didn’t see any sign of phosphine. According to their results, if there is any phosphine present in Venus’s atmosphere at all, it’s a maximum of about 0.8 parts phosphine per billion parts everything else, much smaller than the initial estimate.

Pointing SOFIA’s telescope at Venus was a challenge in and of itself. The window during which Venus could be observed was short, about half an hour after sunset, and the aircraft needed to be in the right place at the right time. Venus also goes through phases similar to the Moon, making it difficult to center the telescope on the planet. Add in its proximity to the Sun in the sky — which the telescope must avoid — and the situation quickly became tense.

“You don’t want sunlight accidentally coming in and shining on your sensitive telescope instruments,” Cordiner said. “The Sun is the last thing you want in the sky when you’re doing these kinds of sensitive observations.”

Despite the fact the group did not find phosphine after the stressful observations, the study was a success. Along with complementary data from other observatories that vary in the depths they probe within Venus’s atmosphere, the SOFIA results help build the body of evidence against phosphine anywhere in Venus’s atmosphere, from its equator to its poles.

SOFIA was a joint project of NASA and the German Space Agency at DLR. DLR provided the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley managed the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft was maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014 and concluded its final science flight on Sept. 29, 2022.

Magnetic Fields Help Black Holes Reach Deeper Into Galaxies

by Anashe Bandari

Black holes potentially have an even larger influence on the galaxies around them than we thought. And the Stratospheric Observatory for Infrared Astronomy (SOFIA) provided a new way to look at their impact.

Active galactic nuclei (AGN) — the central region of a galaxy, which houses its supermassive black hole — are classified by how strong of a jet they produce, shooting matter away at near light speed. Since the jets are mostly visible at radio wavelengths, they are described as either radio loud or radio quiet.

Artist’s conception of Cygnus A, surrounded by the torus of dust and debris with jets launching from its center
Artist’s conception of Cygnus A, surrounded by the torus of dust and debris with jets launching from its center. Magnetic fields are illustrated trapping dust near the supermassive black hole at the galaxy’s core. This initial study motivated the larger comparison of radio loudness to polarization and was included in the composite data set. Credit: NASA/SOFIA/Lynette Cook

“We see that some AGN have very powerful radio jets and some don’t, even though all AGN are intrinsically the same — they all have a supermassive black hole in the center and accrete mass,” said Enrique Lopez-Rodriguez, a research scientist at Stanford University’s Kavli Institute for Particle Astrophysics and Cosmology and lead author on the new SOFIA finding. “We don’t understand why some of them are so powerful, and some of them are not.”

Now, using SOFIA, Lopez-Rodriguez and his team have found that the polarization of infrared light from AGN also increases with their radio loudness, providing a new way to study black hole characteristics.

Motivated by the 2018 SOFIA discovery that the infrared light from the strongest known radio-loud AGN, Cygnus A, was highly polarized, the researchers developed a follow-up observation program with SOFIA to determine whether there’s a relationship between infrared polarization and radio loudness, and if so, why. They looked at the magnetic fields of a total of nine AGN, four of them radio loud and five radio quiet.

From SOFIA observations of light polarization, astronomers can deduce the structure of the magnetic field in the region. In the AGN sample Lopez-Rodriquez and his team studied, these polarizations show that in radio-loud AGN — AGN with strong jets — there’s a donut-shaped magnetic field perpendicular to the jets, along the equator of the AGN. That only radio-loud AGN have such a strong toroidal magnetic field indicates that the field is helping to transfer energy inward, feeding the black hole with matter coming from the host galaxy. The stronger the jets, the stronger the magnetic field, and the more energy there is in the system.

The group was surprised by the strength of the result.

“We were hoping for it, but we weren’t expecting such a nice correlation,” Lopez-Rodriguez said. “There’s so much physics behind it that we don’t understand, and future hydromagnetic models are required.”

Though a lot of science behind these objects remains unexplained, the result implies that black holes are potentially affecting galaxy evolution and jet production quite a bit more than astronomers previously realized. While astronomers typically consider gravity as the only force influencing supermassive black holes, this work shows that magnetic fields can aid in bridging the interface between black holes and matter in their host galaxy. With the help of these magnetic fields, black holes can impact not only the matter immediately around them, but can also work at even larger distances within the galaxy.

SOFIA was a joint project of NASA and the German Space Agency at DLR. DLR provided the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Center in California’s Silicon Valley managed the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft was maintained and operated by NASA’s Armstrong Flight Research Center Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014 and concluded its final science flight on Sept. 29, 2022.