As we near the end of the year—a difficult one for most everyone on the planet—what were the biggest stories related to the search for life beyond Earth? It seems fitting that we start with a loss—of the Arecibo Telescope in Puerto Rico.
The 305-meter-wide radio telescope, which opened for business in 1963, experienced a catastrophic failure when two supporting cables broke—one in August and another in November. The suspended instrument platform fell and crashed into the giant dish on December 1. Arecibo was the world’s largest telescope for decades, and was used for many studies, many of them ground-breaking. These included discovery of the first exoplanet (orbiting the pulsar PSR B1257+12) in 1992, the detection and characterization of many near-Earth asteroids, and investigating the nature of Fast Radio Bursts, which have led to heated discussion about whether these puzzling objects might be artificial in origin. Arecibo was also the site from which an interstellar radio message was sent out in 1974, with—at least so far—no answer back. And movie aficionados will recall that Contact and GoldenEye both used the telescope as an unforgettable film location. The loss for radio astronomy is devastating. We will dearly miss Arecibo’s ability to detect anomalies in the radio sky, which may be key to finding technologically advanced extraterrestrial life. The question now is how this loss can be replaced.
On the positive side were several exciting spacecraft missions launched in 2020. China’s Chang’e-5 expedition closed out the year by bringing back rocks and soil from the lunar Ocean of Storms. That should give us a better understanding of the Moon’s history, as the probe collected samples thought to be much younger than those returned by Apollo astronauts who landed in similar flat plains.
Even more exciting from an astrobiological perspective were the multiple missions launched to Mars this year. The most exciting of these is NASA’s Perseverance Rover, the first leg of a campaign to return samples from Mars. The rover will collect rocks and sediment and place them in sealed tubes on the surface, to be retrieved and returned to Earth by a follow-up mission within a few years. The expectation is that we may find hints of past or present life once that cache is analyzed. Perseverance and two other Mars missions, sent by China and the United Arab Emirates, will reach the Red Planet in February. Unfortunately, the second part of Europe’s ExoMars mission—more explicitly focused on astrobiology—had to be postponed until 2022. But once the Rosalind Franklin rover arrives on Mars in June 2023, it will apply the best tools yet to the problem of determining whether traces of life exist on Mars.
The most controversial discovery of the year in regard to astrobiology was the claimed detection of phosphine in the lower clouds of Venus, which hinted at the presence of an aerial biosphere. Based on its hellish environmental conditions, most researchers would have considered that planet utterly lifeless. The attention suddenly paid to Venus was personally gratifying, because I published about the possibility of Venusian cloud life more than a decade ago. The paper did indeed stir up a lot of initial excitement, but how should we evaluate the claim a few months later?
The phosphine detection itself—though challenged from many sides—still stands, although at a lower abundance than initially claimed. My own first reaction to the claim may have been a bit optimistic. But finding phosphine—a molecule indicative of biology on Earth—is still astounding, especially because the gas had not been detected previously on any other terrestrial planet. But it’s far too early to claim we’ve found life on Venus. There are many unknowns about our “twin planet,” which remains largely alien to us. Many processes and chemical reactions are likely occurring in the Venusian atmosphere and on the surface that we don’t yet understand. At present, many of our conclusions are based on models, not actual observations. And the barriers to life in the Venusian atmosphere are formidable: How could it cope with the difficulties of being airborne, along with the hyperacidity, extreme lack of water, and a possible lack of critical nutrients? So, important as this claim is, the year ends with no clear answer—just a hope for future investigations.