The European Space Agency’s Solar Orbiter is about to get a rare celestial treat. It will be the sixth spacecraft to accidentally cross the tail of a comet. Although its scientific mission was not expected to start just yet, the serendipitous encounter with the comet made the science team change their plan.
The probe is currently in the wake of Comet ATLAS, a recently discovered comet that fragmented at its approached the Sun. Scientists have turned on four of the Solar Orbiter's suite of instruments to learn more about the comet’s composition as it passes through its tail.
Comets are mostly made of ice so when they approach the Sun they begin to evaporate leaving a trail of fine particles behind, sometimes extending millions of kilometers away from the comet itself. This is its "tail".
All previous crossings of comets' tails by spacecraft have only been discovered after the event, but having the knowledge that the Solar Orbiter would pass through ATLAS's tail in advance allowed the science team to prepare it for the encounter. They were alerted by Professor Geraint Jones of the UCL Mullard Space Science Laboratory. Jones has a history of discovering such encounters, having found three in the data from the ESA/NASA Ulysses Sun-studying spacecraft.
“An unexpected encounter like this provides a mission with unique opportunities and challenges, but that’s good! Chances like this are all part of the adventure of science,” said ESA Director of Science Günther Hasinger in a statement.
Solar Orbiter's main mission to the Sun is to study the property of the solar wind and observe for the first time the polar regions of our star. Its instruments will hopefully detect how the ions and dust released by the comet are affected by the solar wind, the stream of charged particles released by the Sun.
“With each encounter with a comet, we learn more about these intriguing objects. If Solar Orbiter detects Comet ATLAS's presence, then we'll learn more about how comets interact with the solar wind, and we can check, for example, whether our expectations of dust tail behavior agree with our models,” Professor Jones said. “All missions that encounter comets provide pieces of the jigsaw puzzle.”
Professor Jones is also the principal investigator on the Comet Interceptor project. This mission will consist of three spacecraft and is scheduled for launch in 2028, aiming to intercept yet-to-be-discovered interstellar comets like comet Borisov or another interstellar object like ‘Oumuamua.