The main goal of the European Space Agency (ESA) Gaia satellite is to observe more than a billion stars to create the most accurate and complete map of the Milky Way. The mission recently released a data collection detailing more than 1.8 billion stars and several million galaxies and quasars.
The new version of Gaia also includes precise positions and velocities of more than 150,000 asteroids in our solar system, a significant fraction of the 1.2 million asteroids we know today. The satellite also measured spectra of reflected sunlight from about 60,000 asteroids, a factor of 10 more than previously available. The rich data set allows scientists to dig deeper into the history of the solar system.
Asteroids hold a key to the history of the solar system. Their orbits and compositions tell a story of planetary migrations, chaotic orbital evolutions, and past collisions. Accurate orbit calculations allow scientists to match asteroids to meteorites that have fallen to Earth, the composition of which can be measured in detail in a laboratory. Some categories of asteroids known as “primitive” have even preserved the composition of the protoplanetary disk from which the planets of our solar system and other celestial bodies formed.
Therefore, to understand the solar system, it is imperative to take stock of the rocky mess by looking for new asteroids and keeping track of the old ones.
All but a tiny fraction of the asteroids in the new Gaia data release are familiar ones. “Gaia is not a powerful machine for asteroid detection, but it is very powerful for characterizing them,” said Paolo Tanga, a planetary scientist at the Observatoire de la Côte d’Azur in France who led a study on the asteroid survey.
Gaia measures the orbital positions and 3D velocities and brightness of asteroids. It also measures reflectance spectra for the brighter objects, which will help provide insight into the shape and rotation of asteroids.
On average, Gaia measures asteroid positions and trajectories about a thousand times more accurately than previously available, allowing researchers to calculate more accurate orbits. This precision allows scientists to detect binary asteroids in the main belt by looking for tiny, periodic oscillations in their positions.
Binary asteroid tracking is important because certain pairs allow asteroid density to be measured. “The bulk densities of 30 or 40 asteroids are well known, and for the rest we only have an indirect estimate,” Tanga said.
Scientists have said Gaia could play an important role in characterizing the Yarkovsky effect, a complex force that governs asteroid dynamics. The effect (sometimes called Yarkovsky drift) explains how solar radiation and an object’s rotation affect an asteroid’s orbit.
“The Yarkovsky effect is quite complicated because it depends on many different physical parameters,” said Sarah Greenstreet, a planetary scientist at the University of Washington. One of the key parameters is the size of an asteroid.
The effect was measured for 234 near-Earth asteroids – but not for a single member of the main belt. Gaia could measure the Yarkovsky effect for main-belt asteroids ranging in size from 2 to 5 kilometers. “Gaia can help us better understand how asteroids move in the solar system and how things can move from the main asteroid belt into orbits that bring them closer to Earth,” Greenstreet said.
The Yarkovsky effect is also responsible for the dispersal of asteroid families, or clusters of asteroids with similar orbital elements thought to be fragments of past asteroid collisions. Accurate orbit calculations and reflection spectra will help researchers identify distant family members and figure out how their current orbits have evolved.
time for some science
Searching for binary asteroids and measuring the Yarkovsky effect are just two of many potential projects awaiting scientists using Gaia data. Tanga also enjoys using precise positions and velocities to predict when asteroids will pass in front of stars. He said observations of such occultations, made by experts and crowd-sourced science alike, are invaluable as they have led to much improved measurements of asteroid shapes and sizes.
Gaia’s next catalog, due out in a few years, will likely double the number of asteroids studied, contain more information about their shape and rotational properties, and likely include data on comets as well.
—Jure Japelj (@JureJapelj), science writer
Quote: Japelj, J. (2022), Galaxy Mapper Tracks Asteroids Closer to Home, Eos, 103, https://doi.org/10.1029/2022EO220320. Published on July 14, 2022.
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