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NASA’s Dawn probe is about to get into its closest orbit yet around the dwarf planet Ceres

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But it’ll soon run out of fuel in the fall

An artistic rendering of Dawn at Ceres
Image: NASA

NASA’s Dawn spacecraft, which is orbiting around the dwarf planet Ceres in the asteroid belt, is about to get closer to this celestial object than ever before. In early June, Dawn will get to its final orbit around Ceres — an elliptical path that will take the probe 10 times closer to the surface than it’s ever been. The spacecraft will collect new, more precise data from this orbit until its fuel runs out sometime this fall.

That will bring an end to the Dawn mission, which has been going strong for over a decade now. Launched in 2007, the Dawn spacecraft traveled for years to the asteroid belt between Mars and Jupiter, first visiting an asteroid named Vesta in 2011. After orbiting Vesta for a year, the probe then traveled to Ceres, entering the dwarf planet’s orbit in March 2015. Dawn spent more than a year studying the object. The mission team hoped to extend the spacecraft’s mission, which officially ended in June 2016, by sending it to visit another object in the asteroid belt called Adeona. However, NASA decided to keep Dawn where it was and continue investigating Ceres.

During this last phase of the mission, the spacecraft will, at times, come within 21.7 miles (35 kilometers) of the dwarf planet. Getting so close will allow Dawn to scan the surface at a very high resolution, which is critical for figuring out what Ceres is made of. On board the spacecraft is an instrument that detects neutrons and highly energetic light called gamma rays coming from the surface of Ceres. These particles hold clues about the types of elements that are within the dwarf planet and their signals are much easier to detect the closer you get to the surface. The measurements could help researchers better understand how Ceres evolved over time.

“This will help us to really understand the bulk composition of Ceres — what the body is made of, what it started with, and how the geological process has modified that,” Carol Raymond, the principal investigator of the Dawn mission, tells The Verge.

One of the first images returned from Dawn in more than a year, taken on May 16th, 2018 from a height of 270 miles above the surface of Ceres
Image: NASA

Figuring out how to get into such a tight, elliptical orbit was a challenge for the mission team, though. Dawn has only ever flown circular paths around Ceres before. Plus it’s hard to remain in a stable orbit so close around a dwarf planet. The object is big enough to have a decent gravitational pull, but it’s still fairly small, so any orbiting spacecraft is much more easily affected by outside forces. Highly energetic particles coming from the Sun can push and pull on Dawn, knocking it off its path. “It was the question of how low can you go and how long can you last,” says Raymond.

The Dawn team ultimately found a way to get into a good orbit where the probe will remain for up to 50 years. But the spacecraft won’t be in communication with Earth for much longer. When its fuel runs out, the vehicle won’t be able to orient its solar panels toward the Sun, and it will eventually run out of power.

It’s unclear what will happen to Dawn after the 50 years is up, since the team only did analyses of the orbit up until that point. However, Raymond says the spacecraft will probably stick around Ceres as a permanent satellite. “The expectation is it will just continue without any change,” she says. “And at some point in the future when we go back to Ceres, we may be able to spot it still circling.”