Hubble Asteroid Hunter

Welcome to our project! The idea of the Hubble Asteroid Hunters is to identify asteroid trails in archival images from the NASA/ESA Hubble Space Telescope, which are stored in the European Space Agency (ESA)'s Hubble Science archive and accessible at ESA's ESASky Portal.

Sometimes when we are observing stars in the Milky Way or far away galaxies asteroids orbiting the Sun a few tens or hundreds of millions of kilometres away happen to pass through the observed field and appear in the foreground of telescope images. For example, the image below is part of a survey made with the Hubble Space Telescope called the Hubble Frontier Fields and it shows thousands of distant galaxies, as well as a few stars from our own Milky Way. Most of the galaxies appear tiny and blue, but the image also contains some impressive spiral galaxies and huge red elliptical galaxies.

The image also shows trails of asteroids that were passing by at the time of the observation. These appear curved due to an effect called parallax. As the Hubble Space Telescope orbits around Earth and images a patch of the sky for a certain amount of time, asteroids will appear to move along an arc with respect to the more distant background stars and galaxies. Because of this parallax effect, asteroids that were closer to us at the time appear passing more rapidly, and thus leaving longer trails in the images, compared to more distant objects.

This image is a mosaic of many exposures, which is why some asteroids appear multiple times. In this mosaic, 20 asteroid trails are visible, belonging to 7 unique objects; five of these were new discoveries. The positions of the asteroid trail in the images allow us to derive what astronomers call the asteroid's "ephemeris" (its position and velocity over time), since we know the time when the image was taken. By observing the same asteroid in multiple exposures, we can refine its ephemeris and therefore can predict better their future orbit.

[Credits: NASA, ESA, and B. Sunnquist and J. Mack (STScI) (CC BY-SA 4.0)]

In this project, we use archival images made by the Hubble Space Telescope to find asteroids observed by chance. The ESASky team compared the observation epoch and field of view of these images with the computed orbits of asteroids, to identify possible observations. The positions predicted by the algorithm, nevertheless, have some associated uncertainty because the ephemerides are not always known to great precision. This uncertainty increases with the amount of time between the last observation date and the date we predict the position for. Identifying the asteroids in the images (if present) and marking the exact position of their trail allows us to update the ephemerides and help us better characterise these objects.

Instead of a coloured mosaic (as shown in the previous picture) we use single exposures.

These observations will be used by the International Astronomical Union's Minor Planet Center to compute the orbits and update the ephemerides of asteroids to better predict their future trajectories.

Identifying asteroids in archival observations is essential to measure their trajectories with higher accuracy and to follow them up in order to further characterise their sizes, shapes and masses, so that we can better understand the asteroid population and potential threats to Earth can be identified. The identification of asteroids will also be used to train a neural network to recognise such objects in images, by scanning the whole HST archive for images of asteroids, including both objects whose orbits are known and those previously unknown to us that were serendipitously observed by Hubble Space Telescope.

Image credits:
Logo - ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA (CC BY-SA 4.0)
Background - NASA/JPL-Caltech/T.Pyle (IPAC)