Mercury is the closest planet to our Sun, ranging from 46 million km (28.58 million mi) at perihelion to 69.82 million km (43.38 million mi) at aphelion. Because of its proximity, Mercury is strongly influenced by the steam of plasma constantly flowing from the Sun to the edge of the Solar System (aka. solar wind). Beginning with the Mariner 10 mission in 1974, robotic explorers have been sent to Mercury to measure how solar wind interacts with Mercury’s magnetic field to produce whistler-mode chorus waves – natural radio emissions that play a key role in electron acceleration in planetary magnetospheres.
In addition to being the cause of geomagnetic storms and auroras in planetary atmospheres, these waves also lead to electromagnetic vibrations at the same frequencies as sound, producing chirps and whistles. In a recent study, an international research team consulted data from the BepiColombo International Mercury Exploration Project, which gathered data on Mercury’s magnetosphere during its first and second flyby. Their results are the first direct probing of chorus waves in Mercury’s dawn sector, which showed evidence of possible background variations in magnetic field.
Alas, all good things must come to an end. In 2020, Arianespace and the ESA signed contracts for the rocket’s last eight launches before the Ariane 6 (a heavier two-stage launcher) would succeed it. The Ariane 5‘s final flight (VA261) lifted off from Europe’s Spaceport at 06:00 PM EST (03:00 PM PST) on July 5th, 2023, and placed two payloads into their planned geostationary transfer orbits (GTO) about 33 minutes later. On the downside, this means that the ESA is effectively out of launch vehicles until the Ariane 6 makes its debut next year.
BepiColombo’s stunning close pass by Mercury on Thursday provides a prelude of what’s to come.
Welcome (briefly) to Mercury, with a planetary flyby hinting at more to come. The joint European Space Agency/Japanese Aerospace Agency’s BepiColombo spacecraft treated us to just that on Thursday, June 23rd, passing just 200 kilometers from the surface of the innermost world at 9:44 Universal Time (UT). During that brief encounter, BepiColombo got a brief glimpse of its final destination.
BepiColombo recently had its first close flyby of Mercury, its eventual mission target, and got to snap some pictures to commemorate the event. Even at this early stage of the mission, these images are some of the clearest we have ever had of the innermost planet.
BepiColombo made a quick visit to Venus in August and is on to its next rendezvous. On October 1st it’ll perform a flyby of Mercury, the spacecraft’s eventual destination. This visit is just a little flirtation—one of six—ahead of its eventual orbital link-up with Mercury in late 2025.
The quick visit will yield some scientific results, though, and they’ll be just a taste of what’s ahead in BepiColumbo’s one-year mission to Mercury.
So much in the astronomy community revolves around the decadal survey. Teams of dozens of scientists put hundreds of hours developing proposals that eventually try to impact the recommendations of the survey panel that influence billions of dollars in research funding over the following decade. And right now is the prime time to get those proposals in. One of the most ambitious is sponsored by a team led by researchers at John Hopkins University Applied Physics Laboratory (APL). Their suggestion – it’s time to land on Mercury.
Astronomers have an excellent habit of naming large projects after deserving contributors to their field. From Nancy Grace Roman to Edwin Hubble, some of the biggest missions are named after space exploration pioneers. When ESA and JAXA sat down to figure out a name for their new Mercury probe, they would have come across an important name early in their research – Giuseppe “Bepi” Colombo – the man who helped plan the Mariner 10 Mercury mission.
When Longfellow wrote about “ships passing in the night” back in 1863, he probably wasn’t thinking about satellites passing near Venus. He probably also wouldn’t have considered 575,000 km separation as “passing”, but on the scale of interplanetary exploration, it might as well be. And passing is exactly what two satellites will be doing near Venus in the next few days – performing two flybys of the planet within 33 hours of each other.
In the image, the Earth hangs serenely in between BepiColumbo’s magnetometer boom (on the right) and its medium-gain antenna (on the left).
But the Earth flyby wasn’t without its tense moments. The spacecraft relies on solar power, and during the loop around Earth it had to spend some time in our planet’s shadow – and out of the sun. To prepare, the mission scientists made sure that BepiColombo was fully charged and nice and warm before the maneuver.
And on April 10, the date of the flyby, it all went swimmingly.
The spacecraft is on a long, winding journey sunwards towards the smallest planet in the solar system, making loop after loop first around Earth, then Venus a couple times, then Mercury itself half a dozen times before parking itself in orbit. The frequent loops are necessary because at launch BepiColombo was traveling at the same speed as the Earth in its orbit (29.78 km/s), and needs to match that of Mercury (47.36 km/s), and it does so by borrowing some energy from the planets themselves.
Once BepiColombo reaches Mercury, it will separate into two individual probes: the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter. The twin orbiters will attempt to answer several challenging riddles about the planet nearest to the sun, like the origins of Mercury’s faint-but-still-there magnetic field and atmosphere, and the craters pitting its surface.
But it will take a long time to get there. BepiColombo’s final arrival at Mercury isn’t scheduled until December of 2025, showing how reaching the inner planets of our system can be sometimes more difficult than journeys outward – it turns out that doing planetary dances is more challenging than you might think.