An artist's conception of an NEO asteroid orbiting the Sun. Credit: NASA/JPL.
Last July, a once-in-a-lifetime event happened. Not the good kind; the football-field-sized-asteroid near-miss kind. And that near miss is the catalyst for a renewed effort from NASA to detect more dangerous space-rocks that might threaten Earth.
Last summer’s near-miss asteroid was named 2019 OK, and it passed within about 77,000 km (48,000 miles) of Earth. It managed to slip past all of our detection methods and came within 0.19 lunar distances to Earth. In astronomical terms, that is remarkably close.
We only had 24 hours notice that the asteroid was coming, thanks to a small telescope in Brazil that spotted it. That near miss has sparked a renewed conversation on planetary defense and on NASA’s role in it.
It also left people wondering how this could happen.
Artist's impression of a Near-Earth Asteroid passing by Earth. Credit: ESA
In February of 2014, NASA put out the call for submissions for the thirteenth mission of their Discovery Program. In keeping with the program’s goal of mounting low-cost, highly focused missions to explore the Solar System, the latest program is focused on missions that look beyond Mars to new research goals. On September 30th, 2015, five semifinalists were announced, which included proposals for sending probes back to Venus, to sending orbiters to study asteroids and Near-Earth Objects.
Among the proposed NEO missions is the Near Earth Object Camera, or NEOCam. Consisting of a space-based infrared telescope designed to survey the Solar System for potentially hazardous asteroids, the NEOCam would be responsible for discovering and characterizing ten times more near-Earth objects than all NEOs that have discovered to date.
If deployed, NEOCam will begin discovering approximately one million asteroids in the Main Belt and thousands of comets in the course of its 4 year mission. However, the primary scientific goal of NEOCam is to discover and characterize over two-thirds of the asteroids that are larger that 140 meters, since it is possible some of these might pose a threat to Earth someday.
Artist’s concept of the NEOCam spacecraft, a proposed mission for NASA’s Discovery program that would search for potentially hazardous near-Earth asteroids. Credit: NASA/JPL-Caltech
The technical term is Potentially Hazardous Objects (PHO), and it applies to near-Earth asteroids/comets that have an orbit that will allow them to make close approaches to Earth. And measuring more than 140 meters in diameter, they are of sufficient size that they could cause significant regional damage if they struck Earth.
In fact, a study conducted in 2010 through the Imperial College of London and Purdue University found that an asteroid measuring 50-meters across with a density of 2.6 grams per cubic centimeter and a speed of 12.7 kps could generate 2.9 Megatons of airburst energy once it passed through our atmosphere. To put that in perspective, that’s the equivalent of about nine W87 thermonuclear warheads!
By comparison, the meteor that appeared over the small Russian community of Chelyabinsk in 2013 measured only 20 meters across. Nevertheless, the explosive airbust caused by it entering our atmosphere generated only 500 kilotons of energy, creating a zone of destruction tens of kilometers wide and injuring 1,491 people. One can imagine without much effort how much worse it would have been had the explosion been six times as big!
What’s more, as of August 1st, 2015, NASA has listed a total of 1,605 potentially hazardous asteroids and 85 near-Earth comets. Among these, there are 154 PHAs believed to be larger than one kilometer in diameter. This represents a tenfold increase in discoveries since the end of the 1990s, which is due to several astronomical surveys being performed (as well as improvements in detection methods) over the past two and a half decades.
The NEOCam sensor (right) is the lynchpin for the proposed Near Earth Object Camera, or NEOCam, space mission (left). Credit: NASA/JPL-Caltech
As a result, monitoring and characterizing which of these objects is likely to pose a threat to Earth in the future has been a scientific priority in recent years. It is also why the U.S. Congress passed the “George E. Brown, Jr. Near-Earth Object Survey Act” in 2005. Also known as the “NASA Authorization Act of 2005”, this Act of Congress mandated that NASA identify 90% of all NEOs that could pose a threat to Earth.
If deployed, NEOCam will monitor NEOs from the Earth–Sun L1 Lagrange point, allowing it to look close to the Sun and see objects inside Earth’s orbit. To this, NEOCam will rely on a single scientific instrument: a 50 cm diameter telescope that operates at two heat-sensing infrared wavelengths, to detect the even the dark asteroids that are hardest to find.
By using two heat-sensitive infrared imaging channels, NEOCam can also make accurate measurements of NEO and gain valuable information about their sizes, composition, shapes, rotational states, and orbits. As Dr. Amy Mainzer, the Principal Investigator of the NEOCam mission, explained:
“Everyone wants to know about asteroids hitting the Earth; NEOCam is designed to tackle this issue. We expect that NEOCam will discover about ten times more asteroids than are currently known, plus millions of asteroids in the main belt between Mars and Jupiter. By conducting a comprehensive asteroid survey, NEOCam will address three needs: planetary defense, understanding the origins and evolution of our solar system, and finding new destinations for future exploration.”
Dr. Mainzer is no stranger to infrared imaging for the sake of space exploration. In addition to being the Principal Investigator on this mission and a member of the Jet Propulsion Laboratory, she is also the Deputy Project Scientist for the Wide-field Infrared Survey Explorer (WISE) and the Principal Investigator for the NEOWISE project to study minor planets.
She has also appeared many times on the History Channel series The Universe, the documentary featurette “Stellar Cartography: On Earth”, and serves as the science consultant and host for the live-action PBS Kids series Ready Jet Go!, which will be debuting in the winter of 2016. Under her direction, the NEOCam mission will also study the origin and ultimate fate of our solar system’s asteroids, and finding the most suitable NEO targets for future exploration by robots and humans.
Proposals for NEOCam have been submitted a total of three times to the NASA Discovery Program – in 2006, 2010, and 2015, respectively. In 2010, NEOCam was selected to receive technology development funding to design and test new detectors optimized for asteroid and comet detection and discovery. However, the mission was ultimately overruled in favor of the Mars InSight Lander, which is scheduled for launch in 2016.
As one of the semifinalists for Discovery Mission 13, the NEOCam mission has received $3 million for year-long studies to lay out detailed mission plans and reduce risks. In September of 2016, one or two finalist will be selected to receive the program’s budget of $450 million (minus the cost of a launch vehicle and mission operations), and will launch in 2020 at the earliest.
In related news, NASA has confirmed that the asteroid known as 86666 (2000 FL10) will be passing Earth tomorrow. No need to worry, though. At its closest approach, the asteroid will still be at a distance of 892,577 km (554,000 mi) from Earth. Still, every passing rock underlines the need for knowing more about NEOs and where they might be headed one day!
On the morning of February 15, 2013, people in western Russia were dazzled by an incredibly bright meteor blazing a fiery contrail across the sky. A few minutes later a shockwave struck, shaking the buildings and blowing out windows. 1,500 people went to the hospital with injuries from shattered glass. This was the Chelyabinsk meteor, a chunk of rock that struck the atmosphere going almost 19 kilometers per second. Astronomers estimate that it was 15-20 meters across and weighed around 12,000 metric tonnes.
Here’s the crazy part. It was the largest known object to strike the atmosphere since the Tunguska explosion in 1908. Catastrophic impacts have shaped the evolution of life on Earth. Once every 65 million years or so, there’s an impact so destructive, it wipes out almost all life on Earth. The bad news is the Chelyabinsk event was a surprise. The asteroid came out of nowhere. We need to find all the potential killer asteroids, and understand what risks we face.
“I’m Ned Wright…”
That’s Dr. Ned Wright. He’s a professor of physics and astronomy at UCLA, and the Primary Investigator for the Wide-field Infrared Survey Explorer mission; a space telescope that looks for low temperature objects in the infrared spectrum.
“I think the best way to protect the Earth from asteroids is to get out and look very assiduously to find all the hazardous asteroids. Although astronomers have been finding and cataloging asteroids for decades, we still only have a fraction of the dangerous asteroids tracked. The large continent destroyers have mostly been found, but there’s a whole class of smaller, city killers out there, and they’re almost entirely unknown. There are… these dark asteroids that may not be the most dominant part of the population but they certainly can be a very hazardous subset, it’s important to do the observations in the infrared. So you actually, instead of looking for the ones that reflect the most light, you look for the ones that have the biggest area and therefore the ones that are the heaviest and can do the most damage. And so, I think that an infrared survey is the way to go.”
“In the infrared wavelengths, we can find these objects because they’re large, not because they’re bright. And to really do this right, we need a space-based infrared observatory capable of surveying vast areas of the sky, searching for anything moving.”
The WISE mission has been offline for a few years, but WISE is actually being reactivated right now to look for more Near Earth Objects, so we’re currently cooled down to 93 K, and when we get to 73 K, which is where we were when we turned off in 2011 we’ll probably be able to go out and find more Near Earth Objects.
Note: this interview was recorded in November, 2013. WISE resumed operations in December 23, 2013
Artist’s impression of the WISE satellite
But to really find the vast majority of dangerous asteroids, you need a specialized mission. One proposal is the Near Earth Asteroid Camera, or NEOCam because it’d be much better to have a telescope that was slightly colder than the 73 K WISE is with coolant, and you can do that by getting away from the Earth. and so the NEOcam telescope is designed to go a million and a half kilometers from the Earth and therefore it would be quite cold, about 35 K and at that temperature, it can operate longer into the infrared and do a very sensitive survey for asteroids.
NEOCam is just one idea. There’s also the Sentinel proposal from B612 Foundation. It’s also an infrared survey and it would go into an orbit like Venus’ orbit, so it would be hundreds of millions of km away from Earth, but not orbiting around Venus, because that would be too hot as well and then with an infrared telescope, it would survey for asteroids.
NEOCam and Sentinel would operate for years, scanning the sky in the infrared to find all of the really hazardous asteroids. You wouldn’t be able to necessarily find the ones the size of the one that hit Chelyabinsk, and so that broke some windows, but it didn’t kill people, didn’t knock buildings down. So that’s definitely a hazard, but not the city destroying hazard that a 100 meter diameter asteroid would be.
We live in a cosmic shooting gallery. Rocks from space impact the Earth all the time, our next dangerous asteroid is out there, somewhere. Let’s build a space-based infrared survey mission so we can find it, before it finds us.
