Last week, NASA decommissioned a nearly 15-year-old spacecraft that discovered 400 near-Earth asteroids and comets, closing an important chapter in the agency’s planetary defense program.
But astronomers saw that the telescope could still detect objects closer to Earth, and NASA reactivated the mission in 2013 for another decade of observations.
Ground controllers at NASA’s Jet Propulsion Laboratory in California sent the final command to the NEOWISE spacecraft on August 8.
The telescope on NEOWISE was relatively modest in size, with a 16-inch (40-centimeter) primary mirror, more than 16 times smaller than the mirror on the James Webb Space Telescope.
WISE, and then the extended mission of NEOWISE, helped scientists estimate there are approximately 25,000 near-Earth objects.
Closely related to the planetary defense program of the agency, NASA last week decommissioned a spacecraft that had been in service for almost 15 years and had found 400 near-Earth asteroids and comets.
The spacecraft’s infrared telescope took millions of pictures while scanning the entire sky 23 times from its low-Earth orbit. Initially, it looked for infrared emissions from stars, asteroids, and galaxies before narrowing its focus to objects in the Solar System.
Acknowledging NEOs.
In December 2009, the Wide-field Infrared Survey Explorer (WISE) spacecraft began its seven-month mission. WISE went into hibernation in 2011 after NASA ran out of frozen hydrogen coolant, which decreased the sensitivity of its infrared detectors. WISE had finished checkouts and concluded its primary all-sky astronomical survey. NASA, however, reactivated the mission in 2013 for an additional ten years of observations after astronomers realized that the telescope was still capable of detecting objects closer to Earth.
NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) was the new name of the mission. Its goal was to locate faint comets and asteroids that are approaching Earth using the spacecraft’s infrared vision.
“We never imagined it would last this long,” stated Amy Mainzer, the principal investigator for NEOWISE from UCLA and the University of Arizona.
The last command was given to the NEOWISE spacecraft on August 8 by ground controllers at NASA’s Jet Propulsion Laboratory in California. At nearly 217 miles (350 kilometers) above Earth, atmospheric drag is causing the spacecraft to decelerate and eventually fall out of orbit. Because of the upper atmosphere’s expansion brought on by increased solar activity, NASA predicts that the spacecraft will reenter the atmosphere and burn up before the end of this year—a few months earlier than planned. The satellite lacks the ability to propel itself into a higher orbit.
Mainzer told Ars, “It was the right time to let it go. The Sun’s just been incredibly quiet for many years now, but it’s picking back up.”.
Most of the near-Earth objects that have been found so far have been found by astronomers using ground-based telescopes. Nonetheless, there is a benefit to using a space-based telescope since the majority of the infrared radiation from faint objects, such as asteroids, is absorbed by Earth’s atmosphere.
Astronomers “predominately seeing sunlight reflecting off the surfaces of the objects” when using ground-based telescopes, according to Mainzer. Scientists can determine the sizes of asteroids by measuring their thermal emissions with NEOWISE. “With relatively few infrared measurements, we can actually get pretty good measurements of size,” the speaker stated.
With a primary mirror that measured 16 inches (40 centimeters), the telescope on NEOWISE was comparatively small—more than 16 times smaller than the mirror on the James Webb Space Telescope. NEOWISE was a good choice for studying large populations of objects, though, because its wide field of view made it possible to search the sky for infrared light sources. The comet officially designated C/2020 F3, or Comet NEOWISE, which became visible to the unaided eye in 2020, was one of the mission’s most well-known discoveries. Large telescopes like Hubble were able to get a closer look as the comet approached Earth.
According to Nicola Fox, associate administrator of NASA’s science mission directorate, “the NEOWISE mission has been an extraordinary success story as it helped us better understand our place in the universe by tracking asteroids and comets that could be hazardous for us on Earth.”.
What is accessible?
The Center for Near-Earth Object Studies reports that 366 near-Earth asteroids and 34 comets were found when the original WISE mission and the extended survey of NEOWISE were combined. Of these, 64 were deemed to be potentially dangerous asteroids, which means they are at least 500 feet (140 meters) in diameter and are located within 4 points 65 million miles (7 points 48 million kilometers) of Earth. To determine whether these objects present a risk of colliding with Earth, astronomers seek to locate and monitor them.
There are more asteroids out there; there are about 2,400 known asteroids that could be dangerous. Ground-based telescopes are only able to conduct surveys during the night, but space-based telescopes have the advantage of being able to observe continuously throughout the day. Certain dangerous asteroids approach Earth from the direction of the Sun. One such example is the house-sized object that exploded in the atmosphere over Chelyabinsk, Russia, in 2013. These types of asteroids are more likely to be discovered by a space telescope.
Scientists were able to estimate the number of near-Earth objects to be about 25,000 thanks to the WISE and later NEOWISE extended mission.
The majority of the objects that NEOWISE did find were just dark, and Mainzer stated that these are the objects that are far more likely to go unnoticed by ground-based telescopes. We can then determine how many people are actually out there much more accurately as a result. “.
