Twilight observations with the Dark Energy Camera made by the US Department of Energy at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF’s NOIRLab, have allowed astronomers to spot three near-Earth asteroids (NEA ) hidden in the glare of the sun. These NEAs are part of an elusive population lurking inside the orbits of Earth and Venus. One of the asteroids is the largest potentially Earth-hazardous object discovered in the past eight years.
An international team using the Dark Energy Camera (DECam) mounted on the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile, a program of NSF’s NOIRLab, has discovered three new near-Earth asteroids (NEA) lurking in the inner solar system, the region interior to the orbits of Earth and Venus. This is a notoriously difficult region for sightings as asteroid hunters have to deal with glare from the sun.
Taking advantage of brief but favorable viewing conditions at dusk, astronomers have found an elusive trio of NEAs. One is a 1.5 kilometer wide asteroid called 2022 AP7, whose orbit could one day place it in Earth’s path. The other asteroids, called 2021 LJ4 and 2021 PH27, have orbits that remain safely completely inside Earth’s orbit. Also of particular interest to astronomers and astrophysicists, 2021 PH27 is the closest known asteroid to the sun. As such it has the strongest general relativity effects of any object in our solar system and during its orbit its surface becomes hot enough to melt lead.
“Our twilight survey scours the area inside the orbits of Earth and Venus looking for asteroids,” said Scott S. Sheppard, astronomer at the Earth and Planets Laboratory at the Carnegie Institution for Science and lead author of the article describing this work. “So far we’ve found two large near-Earth asteroids about 1 kilometer in diameter, a size we call planet killers.”
“There are probably only a few NEAs of similar sizes left to be found, and these large undiscovered asteroids likely have orbits that keep them inside the orbits of Earth and Venus most of the time,” Sheppard said. “Only about 25 asteroids with orbits completely inside Earth’s orbit have been discovered so far due to the difficulty of observing near the sun’s glow.”
Finding asteroids in the inner solar system is a daunting observational challenge. Astronomers have only two brief 10-minute windows each night to survey this area and must deal with bright background skies resulting from glare from the sun. Additionally, these observations are very close to the horizon, meaning astronomers must observe through a thick layer of Earth’s atmosphere, which can blur and distort their observations.
The discovery of these three new asteroids despite these challenges was possible thanks to DECam’s unique observing capabilities. The state-of-the-art instrument is one of the most capable wide-field CCD imagers in the world, giving astronomers the ability to capture large areas of sky with high sensitivity.
Astronomers call observations “deep” if they capture faint objects. When hunting asteroids inside Earth’s orbit, the ability to capture both deep and wide-field observations is a must.
“Large areas of sky are needed because interior asteroids are rare, and deep images are needed because asteroids are faint and you’re fighting bright twilight skies near the sun as well as the distorting effect of Earth’s atmosphere,” Sheppard said. “DECam can cover large areas of the sky at depths impossible to reach with smaller telescopes, allowing us to reach further, cover more sky, and probe the inner solar system in ways never before possible. .”
In addition to detecting asteroids that could potentially pose a threat to Earth, this research is an important step towards understanding the distribution of small bodies in our solar system. Asteroids farther from the sun than Earth are the easiest to detect. For this reason, these more distant asteroids tend to dominate current theoretical models of the asteroid population.
Detecting these objects also allows astronomers to understand how asteroids are transported through the inner solar system and how gravitational interactions and heat from the sun can contribute to their fragmentation.
“Our DECam survey is one of the largest and most sensitive searches ever for objects in Earth’s orbit and near the orbit of Venus,” Sheppard said. “It’s a unique chance to understand what kinds of objects lurk in the inner solar system.”
“After ten years of outstanding service, DECam continues to produce important scientific discoveries while contributing to planetary defense, a crucial service that benefits all of humanity,” said Chris Davis, NSF Program Director for NOIRLab.
The findings are published in The Astronomical Journal.
More information:
Scott S. Sheppard et al, A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus, The Astronomical Journal (2022). DOI: 10.3847/1538-3881/ac8cff
Provided by the Association of Universities for Research in Astronomy (AURA)
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