Gaia revolutionizes asteroid tracking

ESA’s Gaia Space Observatory is an ambitious mission to build a three-dimensional map of our galaxy using high-precision measurements of more than a billion stars. However, on her journey to map distant suns, Gaia is revolutionizing a field much closer to home. By accurately mapping the stars, you’re helping researchers track down lost asteroids.

Using stars to detect asteroids

Gaia traces the galaxy by repeatedly scanning the entire sky. Over the course of her planned mission, she observed each of her more than a billion target stars about 70 times to study how their position and brightness change over time.

The stars are so far from Earth that their movements between images are very small, hence Gaia has to measure their positions so precisely to notice a difference. However, sometimes Gaia detects dim light sources that move considerably from one image in one particular region of the sky to the next, or even are only seen in a single image before disappearing.

To move through Gaia’s field of view so fast, these objects must be located much closer to Earth.

When comparing the positions of these objects with the catalogs of known bodies in the Solar System, many of these objects turn out to be known asteroids. However, some are identified as potentially new detections and are then followed by the astronomy community through the Gaia Tracking Network for Objects in the Solar System. Through this process, Gaia has successfully discovered new asteroids.

Lost objects

These direct observations of asteroids are important to scientists in the solar system. However, Gaia’s highly accurate measurements of star positions provide an even more shocking, but indirect, benefit to tracking asteroids.

“When we look at an asteroid, we look at its motion relative to the background stars to determine its trajectory and predict where it will be in the future,” says Marco Micheli of ESA’s Near-Earth Object Coordination Center. “This means that the more accurately we know the positions of the stars, the more reliably we can determine the orbit of an asteroid passing in front of them.”

In collaboration with the European Southern Observatory (ESO), Marco’s team participated in an observation campaign targeting TC4 2012, a small asteroid that was supposed to pass through Earth. Unfortunately, since the asteroid was first seen in 2012, it had grown weaker and weaker as it receded from Earth, and eventually became unobservable. It was not clear where it would appear in the sky at the time of the next campaign.

“The possible region of the sky where the asteroid could appear was larger than the area that the telescope could observe at the same time,” says Marco. “So we had to find a way to improve our prediction of where the asteroid would be.”

“I looked back at the initial observations from 2012. Since then, Gaia had made more accurate measurements of the positions of some of the stars in the background of the images, and used them to update our understanding of the asteroid’s trajectory and predict where it would be. Appear.”

“We aimed the telescope at the predicted area of ​​the sky using Gaia’s data and found the asteroid on our first attempt.”

“Our next goal was to accurately measure the position of the asteroid, but we had too few stars in our new image to use as a reference. There were 17 stars in an earlier catalog and only four stars measured by Gaia. I did calculations using both data sets.” .

“Later in the year, when the asteroid had been observed several times by other teams and its trajectory was better known, it became clear that the measurements I made with just four Gaia stars had been much more accurate than those used by the 17 stars.” . This was really amazing. “

Keeping the Earth safe

This same technique applies to asteroids that were never lost, allowing researchers to use Gaia’s data to determine their trajectories and physical properties more precisely than ever.

This is helping them update asteroid population models and deepen our understanding of how asteroid orbits develop, for example, by measuring subtle dynamic effects that play a key role in pushing small asteroids into orbits that could see them collide with the Land.

Dancing in the daylight

To make such precise measurements of the positions of other stars, Gaia has a complicated relationship with ours.

Gaia orbits around the second Lagrange point, L2, of the Sun-Earth system. This location keeps the Sun, Earth, and Moon behind Gaia, allowing you to observe a large part of the sky without your interference. It is also in a uniform thermal radiation environment and experiences a stable temperature.

However, Gaia should not completely fall into Earth’s shadow, as the spacecraft still relies on solar energy. Since the orbit around point L2 is unstable, small disturbances can accumulate and watch the spacecraft head toward an eclipse.

Gaia’s flight control team at ESA’s ESOC mission control center in Darmstadt is responsible for making corrections to the spacecraft’s trajectory to keep it in correct orbit and out of Earth’s shadow. They ensure that Gaia remains one of the most stable and accurate spaceships in history. On July 16, 2019, the team successfully performed a crucial maneuver to prevent the eclipse, moving Gaia to the extended phase of her mission and allowing her to continue scanning the sky for several more years.

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