Twilight observations from Cerro Tololo Inter-American Observatory spot three large near-Earth objects lurking in the inner Solar System
From: NoirLab 2226 – Science Release
October 31, 2022 -- Twilight observations with the US Department
of Energy-fabricated Dark Energy Camera at Cerro Tololo Inter-American
Observatory in Chile, a Program of NSF's NOIRLab, have enabled astronomers to
spot three near-Earth asteroids (NEA) hiding in the glare of the Sun. These
NEAs are part of an elusive population that lurks inside the orbits of Earth
and Venus. One of the asteroids is the largest object that is potentially
hazardous to Earth to be discovered in the last eight years.
An international team
using the Dark
Energy Camera (DECam) mounted on the Víctor
M. Blanco 4-meter Telescope at Cerro Tololo Inter-American
Observatory in Chile, a Program of NSF’s NOIRLab, has discovered three new
near-Earth asteroids (NEAs) hiding in the inner Solar System, the region
interior to the orbits of Earth and Venus. This is a notoriously challenging
region for observations because asteroid hunters have to contend with the glare
of the Sun.
By taking advantage of
the brief yet favorable observing conditions during twilight, however, the
astronomers found an elusive trio of NEAs. One is a 1.5-kilometer-wide asteroid
called 2022 AP7, which has an orbit that may someday place it in Earth’s path.
The other asteroids, called 2021 LJ4 and 2021 PH27, have orbits that safely
remain completely interior to Earth’s orbit. Also of special interest to
astronomers and astrophysicists, 2021 PH27 is the closest known asteroid to the
Sun. As such, it has the largest general-relativity effects [1] of any
object in our Solar System and during its orbit its surface gets hot enough to
melt lead.
“Our twilight survey
is scouring the area within the orbits of Earth and Venus for asteroids,”
said Scott S. Sheppard, an astronomer at the Earth and Planets Laboratory of
the Carnegie Institution for Science and the lead author of the paper describing this work.
“So far we have found two large near-Earth asteroids that are about 1
kilometer across, a size that we call planet killers.”
“There are likely
only a few NEAs with similar sizes left to find, and these large undiscovered
asteroids likely have orbits that keep them interior to the orbits of Earth and
Venus most of the time,” said Sheppard. “Only about 25 asteroids with
orbits completely within Earth’s orbit have been discovered to date because of
the difficulty of observing near the glare of the Sun.”
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 have to
contend with a bright background sky resulting from the Sun’s glare.
Additionally, such observations are very near to the horizon, meaning that
astronomers have to observe through a thick layer of Earth’s atmosphere, which
can blur and distort their observations. [2]
Discovering these three
new asteroids despite these challenges was possible thanks to the unique
observing capabilities of DECam. The state-of-the-art instrument is one of the
highest-performance, wide-field CCD imagers in the world, giving astronomers
the ability to capture large areas of sky with great sensitivity. Astronomers
refer to observations as ‘deep’ if they capture faint objects. When hunting for
asteroids inside Earth’s orbit, the capability to capture both deep and
wide-field observations is indispensable. DECam was funded by the US Department
of Energy (DOE) and was built and tested at DOE’s Fermilab.
“Large areas of sky are required because the inner asteroids are rare, and
deep images are needed because asteroids are faint and you are fighting the
bright twilight sky near the Sun as well as the distorting effect of Earth’s
atmosphere,” said Sheppard. “DECam can cover large areas of sky to
depths not achievable on smaller telescopes, allowing us to go deeper, cover
more sky, and probe the inner Solar System in ways never done before.”
As well as detecting
asteroids that could potentially pose a threat to Earth, this research is an
important step toward understanding the distribution of small bodies in our
Solar System. Asteroids that are further from the Sun than Earth are easiest to
detect. Because of that these more-distant asteroids tend to dominate current
theoretical models of the asteroid population. [3]
Detecting these objects
also allows astronomers to understand how asteroids are transported throughout
the inner Solar System and how gravitational interactions and the heat of the
Sun can contribute to their fragmentation.
“Our DECam survey is
one of the largest and most sensitive searches ever performed for objects
within Earth’s orbit and near to Venus’s orbit,” said Sheppard. “This is
a unique chance to understand what types of objects are lurking in the inner
Solar System.”
“After ten years of
remarkable service, DECam continues to yield important scientific discoveries
while at the same time contributing to planetary defense, a crucial service
that benefits all humanity,” said Chris Davis, NSF Program Director for
NOIRLab.
DECam was originally
built to carry out the Dark Energy Survey, which was conducted by the DOE and
the US National Science Foundation between 2013 and 2019.
Notes
[1] Einstein’s
general theory of relativity explains how massive objects warp the fabric of
spacetime and how this influences the motion of objects in the Universe. In our
Solar System, this influence can be directly measured as, for example, the precession
of the orbit of planet Mercury, which cannot be accurately explained using
only Newtonian physics.
[2] Observing
toward the inner Solar System is challenging for ground-based telescopes and
impossible for space-based optical/infrared telescopes like NASA’s Hubble and
JWST telescopes. The intense light and heat of the Sun would fry the sensitive
electronics. For this reason, both Hubble and
JSWT are always pointed away from the Sun.
[3] Atria
asteroids — also known by the Hawaiian term Apohele asteroids — are the
smallest group of near-Earth asteroids. Their orbits have an aphelion (farthest
point from the Sun) smaller than Earth's perihelion (nearest point to the Sun).
More information
Sheppard, S. Tholen,
D., Pokorný, P., Micheli, M., and Dell’Antoniio, I., et al. (2022). “A deep and
wide twilight survey for asteroids interior to Earth and Venus.” Published in
The Astronomical Journal, 164, 168. https://doi.org/10.3847/1538-3881/ac8cff
NSF’s NOIRLab (National
Optical-Infrared Astronomy Research Laboratory), the US center for ground-based
optical-infrared astronomy, operates the international Gemini
Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina,
and KASI–Republic of Korea),
Kitt Peak National Observatory (KPNO),
Cerro Tololo Inter-American Observatory (CTIO), the Community
Science and Data Center (CSDC),
and Vera
C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator
Laboratory). It is managed by the Association of Universities for Research in
Astronomy (AURA) under a
cooperative agreement with NSF and is headquartered in Tucson, Arizona. The
astronomical community is honored to have the opportunity to conduct
astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in
Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and
acknowledge the very significant cultural role and reverence that these sites
have to the Tohono O'odham Nation, to the Native Hawaiian community, and to the
local communities in Chile, respectively.
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