Glare from the Sun is the main reason why telescopes tend to look outward from the Earth, away from the center of our solar system. New research reveals that for telescopic surveys prepared to peer the other way, there’s a lot to be found.
In particular, recent studies reveal near-Earth objects or NEOs, including asteroids that we have never seen before. When it comes to understanding the history of the solar system and the formation of planets, finding and tracking these asteroids could be crucial.
Astronomer Scott Sheppard of the Carnegie Institution for Science in Washington DC has reported on some of the near-Earth objects discovered between Earth and the Sun – and the discoveries are just beginning.
“New telescopic surveys brave sun glare and search sunward for asteroids during twilight,” Sheppard writes in a column for the latest Science log.
“These surveys have found many previously unknown asteroids inside the Earth.”
Discoveries include the first asteroid with an orbit inside Venus (named ‘Ayló’chaxnim 2020 AV2), and the asteroid that currently has the shortest known orbital period around the Sun (named 2021 PH27).
While modeling predicted these asteroids should exist, now telescopes such as the Zwicky Transient Facility Camera in California and the National Science Foundation’s 4-meter Blanco Telescope in Chile – with the Dark Energy Camera (DECam) attached – are beginning to find them. .
These asteroids are classified according to their position: we have the Atiras (with orbits inside the Earth), Vatiras (with orbits inside Venus) and the hypothetical Vulcanoids (with orbits outside interior of Mercury).
What we know from observations of craters on planets and moons is that the number of near-Earth objects has remained stable over the past billion years.
Given their dynamically unstable orbits (about 10 billion years old) and unpredictable motions (caused by exposure to the Sun), this suggests that NEOs somehow recover.
“Motion depends on the asteroid’s rotation, size, albedo, and distance from the Sun,” Sheppard writes. “The smaller an asteroid and the more sunlight it absorbs, the greater its motion.”
These asteroid discoveries should help us better understand their motion and how the number of near-Earth objects has managed to remain stable over such long periods of time. Scientists believe that most near-Earth objects are asteroids that have been dislodged from the main belt between Mars and Jupiter.
However, Sheppard points out that there could also be stable internal reservoirs of NEO, providing a steady supply of Atiras and Vatiras. These can power up and replace asteroids that blast through the wider solar system, crash into a planet, or be annihilated by close contact with the Sun.
The smaller the asteroids, the harder they are to spot of course. Scientists estimate that around 90% of so-called “planet killer” near-Earth objects – those 1 kilometer (0.62 miles) or more in diameter – have already been found.
“The last unknown 1 km NEOs likely have orbits close to the Sun or high inclinations, putting them outside the fields of the main NEO readings,” Sheppard writes.
The perspective was published in Science.