It is a unique encounter. Solar Orbiter, a European spacecraft launched on February 10 and currently on its way to the Sun, has begun to cross the tail of Comet Atlas, an adventure that will take a few days. The artifact was not yet tasked with taking scientific data, but mission experts have worked to ensure that its four most relevant instruments are turned on during the visit.
Solar Orbiter is still in a phase called commissioning, in which scientists and engineers test its operation. It was not until mid-June that the ship should be fully functional, but the discovery of the encounter with the comet has brought this awakening forward. It is not for less, since accidentally crossing the tail of one of these objects is not common in a space mission. It has only happened six times before and in all cases it became known after the event. This will be the first time predicted in advance thanks to Geraint Jones of the UCL Mullard Laboratory for Space Sciences, UK, who realized what was going to happen and warned ESA.
The Solar Orbiter is equipped with a set of ten remote and on-site instruments to investigate the Sun and the flow of charged particles it releases into space: the solar wind. Fortunately, as explained by ESA in a statement, the four instruments on board are also perfect for detecting the comet’s tails because they measure the conditions around the spacecraft, so they could return data on dust grains and charged particles. electrically emitted by the comet. These emissions create the comet’s two tails: the dust tail that remains in the comet’s orbit and the ion tail that points directly at the Sun.
Solar Orbiter, 44 million kilometers from Atlas, has just crossed its ion tail (from May 31 to June 1), and will do the same for the dust tail on June 6. If the ion tail is dense enough, the Solar Orbiter (MAG) magnetometer could detect the variation of the interplanetary magnetic field due to its interaction with the ions in the comet’s tail, while the Solar Wind Analyzer (SWA) could directly capture some of the tail particles.
When Solar Orbiter crosses the dust tail, depending on its density, which is extremely difficult to predict, it is possible that one or more small dust grains will hit the spacecraft at speeds of tens of kilometers per second. While this is not a significant risk, the dust grains will vaporize on impact, forming small clouds of electrically charged gas or plasma, which could be detected by the Radio and Plasma Waves (RPW) instrument.
“An unexpected encounter like this provides a mission with unique opportunities and challenges, but that’s a good thing! Opportunities like this are part of the science adventure, “says Günther Hasinger, ESA’s director of science. “We are ready for whatever Comet ATLAS has to tell us,” adds Daniel Müller, ESA Project Scientist for Solar Orbiter.
And what is the ship going to find? Atlas was discovered on December 28, 2019. During the following months, it lit up so much that astronomers wondered if it would be visible to the naked eye in May. Unfortunately, in early April the comet fragmented. As a result, its brightness also decreased significantly, impeding the show. Additional fragmentation in mid-May further decreased the comet, making it less likely to be detected by Solar Orbiter.
“With each encounter with a comet, we learn more about these intriguing objects. If Solar Orbiter detects the presence of the comet Atlas, we will learn more about how they interact with the solar wind, and we can verify, for example, if our expectations of behavior of the tail of dust agree with our models, “explains the researcher. “All missions encountered with comets provide pieces of the puzzle.”
Solar Orbiter is currently circling our star between the orbits of Venus and Mercury, with its first perihelion taking place on June 15, about 77 million km from the Sun. In the coming years, it will get much closer, within the Mercury’s orbit, about 42 million km from the solar surface. Meanwhile, Comet Atlas will already be there, approaching its own perihelion, expected on May 31, about 37 million km from the Sun.
“This tail crossing is also exciting because it will happen for the first time at such close distances from the Sun, with the comet nucleus within Mercury’s orbit,” says Yannis Zouganelis, assistant scientist on the ESA project for the Solar Orbiter. Looking at an icy object instead of the scorching sun is certainly an exciting and unexpected way for Solar Orbiter to begin its scientific mission. .