Exoplanet-hunting satellite accidentally captures comet outburst
NASA’s Transiting Exoplanet Survey Satellite (TESS) normally focuses its attention on distant stars, but now it’s made a new discovery in our own solar system. While staring off into the depths of interstellar space, the comet 46P/Wirtanen wandered into view, and TESS managed to catch an explosive outburst from the comet in more detail than ever before.
Wirtanen has been observed orbiting the Sun since the 1940s, but last year it made its closest pass to Earth on record. Coming within 30 times the distance to the Moon, this event was among the 10 closest comet flybys within the past 70 years.
Of course, that means astronomers the world over were watching excitedly, ready to study the comet close up with all sorts of instruments. Among them was SOFIA, which found that Wirtanen is carrying “ocean-like” water. TESS was busy doing its own thing, but it became a perfect long-term witness when Wirtanen wandered by.
“TESS spends nearly a month at a time imaging one portion of the sky,” says Tony Farnham, lead author of the study. “With no day or night breaks and no atmospheric interference, we have a very uniform, long-duration set of observations. As comets orbit the Sun, they can pass through TESS’ field of view. Wirtanen was a high priority for us because of its close approach in late 2018, so we decided to use its appearance in the TESS images as a test case to see what we could get out of it. We did so and were very surprised!”
TESS managed to capture an outburst on Wirtanen, which began on September 26, 2018, about three months before the comet’s closest pass to Earth. it started with a flash that lasted an hour or so, then grew brighter more slowly over the next eight hours. After it hit peak brightness, it then faded away over more than two weeks.
Since the satellite takes images every 30 minutes, every stage of this process was captured in more detail than any previous comet outburst. The researchers were even able to estimate that about one million kg (2.2 million lb) of material may have been ejected in the blast.
Exactly what causes these outbursts is unknown, but theories include heat from the Sun igniting pockets of volatile ices on the surface, or the collapse of a cliff. Studying more comet outbursts could help answer the question, and thankfully TESS is on the job.
“We don’t know what causes natural outbursts and that’s ultimately what we want to find,” says Farnham. “There are at least four other comets in the same area of the sky where TESS made these observations, with a total of about 50 comets expected in the first two years’ worth of TESS data. There’s a lot that can come of these data.”
The research was published in the Astrophysical Journal Letters.