A spacecraft on a mission to the sun had a surprise encounter with a comet last year 鈥� and discovered evidence that it may not be a comet after all.
NASA鈥檚 Parker Solar Probe (PSP) was launched in 2018 to study the sun and is currently still in a close orbit, travelling in a region of the solar system often visited by comets.
Jiansen He at Peking University in Beijing, China, and his colleagues checked the orbital trajectory of the spacecraft against a database of comets, looking for potential encounters. The team found that on 2 September 2019, PSP passed a comet called 322P/SOHO at a distance of around 4 million kilometres, which is about 10 times the distance between Earth and the moon.
Advertisement
Examining data from the spacecraft, the researchers saw that its instruments had picked up traces of dust coming off the comet. These instruments were designed to study the solar wind, a steady flow of particles streaming from the sun鈥檚 surface, and spotting the dust was a challenge, says He. 鈥淭he comet activity is relatively weak, while the solar wind background is overwhelming.鈥�
This weak signal explains why the close encounter wasn鈥檛 immediately spotted in PSP鈥檚 data. Without knowledge of the nearby orbits, these dust particles simply appear to be scattered meteoroids from an unknown source, says He.
In fact, the signal was so weak that He believes 322P may not even be a comet, which are usually made of ice, but instead an object with the rocky composition of an asteroid. Its comet-like appearance may arise from the object moving close enough to the sun to be heated to the extent that dust is ejected from its surface. According to the researchers鈥� simulations, if 322P was an icy comet, then it would have been releasing far more dust than they saw.
Chance encounters between spacecraft and comets can offer valuable opportunities to gather information that helps us understand these objects, says Geraint Jones at University College London, who is actively looking for such encounters.
Earlier this year, Jones and his colleagues noticed that the European Space Agency鈥檚 Solar Orbiter probe should have passed through the wake of comet C/2019 Y4 (ATLAS) in June. Jones and his team are still analysing data from the spacecraft, but they presented tentative signs of ATLAS鈥檚 dust at .
Reference:
Sign up to our free Launchpad newsletter for a voyage across the galaxy and beyond, every Friday
