It is a well-known astronomical convention that Earth has only one natural satellite, which is known (somewhat uncreatively) as “the Moon”. However, astronomers have known for a little over a decade that Earth also has a population of what are known as “transient Moons”. These are a subset of Near-Earth Objects (NEOs) that are temporarily scooped up by Earth’s gravity and assume orbits around our planet.
According to a new study by a team of Finish and American astronomers, these temporarily-captured orbiters (TCOs) could be studied with the Large Synoptic Survey Telescope (LSST) in Chile – which is expected to become operational by 2020. By examining these objects with the next-generation telescope, the study’s authors argue that we stand to learn a great deal about NEOs and even begin conducting missions to them.
This coming October, an asteroid will fly by Earth. Known as 2012 TC4, this small rock is believed to measure between 10 and 30 meters (30 and 100 feet) in size. As with most asteroids, this one is expected to sail safely past Earth without incident. This will take place on October 12th, when the asteroid will pass us at a closest estimated distance of 6,800 kilometers (4,200 miles) from Earth’s surface.
That’s certainly good news. But beyond the fact that it does not pose a threat to Earth, NASA is also planning on using the occasion to test their new detection and tracking network. As part of their Planetary Defense Coordination Office (PDCO), this network is responsible for detecting and tracking asteroids that periodically pass close to Earth, which are known as Potentially Hazardous Objects (PHOs)
In addition to relying on data provided by NASA’s Near-Earth Object (NEO) Observations Program. the PDCO also coordinates NEO observations conducted by National Science Foundation (NSF)-sponsored ground-based observatories, as well as space situational awareness facilities run by the US Air Force. Aside from finding and tracking PHOs, the PDCO is also responsible for coming up with ways of deflecting and redirecting them.
The PDCO was officially created in response to the NASA Office of Inspector General’s 2014 report, titled “NASA’s Efforts to Identify Near-Earth Objects and Mitigate Hazards.” Citing such events as the Chelyabinsk meteor, and how such events are relatively common, the report indicated that coordination, early warning and mitigation strategies were needed for the future:
“[I]n February 2013 an 18-meter (59 foot) meteor exploded 14.5 miles above the city of Chelyabinsk, Russia, with the force of 30 atomic bombs, blowing out windows, destroying buildings, injuring more than 1,000 people, and raining down fragments along its trajectory… Recent research suggests that Chelyabinsk-type events occur every 30 to 40 years, with a greater likelihood of impact in the ocean than over populated areas, while impacts from objects greater than a mile in diameter are predicted only once every several hundred thousand years.”
The PDCO was established in 2016, which makes this upcoming flyby the first chance they will have to test their network of observatories and scientists dedicated to planetary defense. Michael Kelley is the program scientist and the NASA Headquarters lead for the TC4 observation campaign, which has been monitoring 2012 TC4 for years. As he said in a recent NASA press statement:
“Scientists have always appreciated knowing when an asteroid will make a close approach to and safely pass the Earth because they can make preparations to collect data to characterize and learn as much as possible about it. This time we are adding in another layer of effort, using this asteroid flyby to test the worldwide asteroid detection and tracking network, assessing our capability to work together in response to finding a potential real asteroid threat.”
In addition, the flyby will be an opportunity to reacquire 2012 TC4, which astronomers lost track of in 2012 when it moved beyond the range of their telescopes. For this reason, people like Professor Vishnu Reddy of the University of Arizona are also excited. A member of the Lunar and Planetary Laboratory, Reddy also leads the campaign to reacquire the asteroid. As he indicated, this flyby will be a chance for collaborative observation.
“This is a team effort that involves more than a dozen observatories, universities and labs across the globe so we can collectively learn the strengths and limitations of our near-Earth object observation capabilities,” he said. “This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications.”
2012 TC4 was originally discovered on Oct. 5th, 2012, by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) at the Haleakala Observatory in Hawaii. After it sped past Earth in that same year, it has not been directly observed since. And while it is slightly larger than the meteor that exploded in Earth’s atmosphere near Chelyabinsk, Russia, in 2013, scientists are certain that it will pass us by at a safe distance.
This is based on tracking data that was collected by scientists from NASA’s Center for Near-Earth Object Studies (CNEOS). After monitoring 2012 TC4 for a period of seven days after it was discovered in 2012, they determined that at its closest approach, the asteroid will pass no closer than 6,800 km (4,200 mi) to Earth. However, it is more likely that it will pass us at distance of about 270,000 km (170,000 mi).
This would place it at a distance that is about two-thirds the distance between the Earth and the Moon. The last time this asteroid passed Earth, it did so at a distance that was one-quarter the distance between the Earth and the Moon. Therefore, the odds of it passing by without incident are even greater this time around. So rather than representing a threat, the passage of this asteroid represents a good chance for research.
As Paul Chodas, the manager of the CNEOS at NASA’s Jet Propulsion Laboratory, stated:
“This is the perfect target for such an exercise because while we know the orbit of 2012 TC4 well enough to be absolutely certain it will not impact Earth, we haven’t established its exact path just yet. It will be incumbent upon the observatories to get a fix on the asteroid as it approaches, and work together to obtain follow-up observations than make more refined asteroid orbit determinations possible.”
By monitoring 2012 TC4 as it flies by, astronomers will be able to refine their knowledge about the asteroid’s orbit, which will help them to predict and calculate future flybys with even greater precision. This will further mitigate the risk posed by PHOs down the road, and help the PDCO to develop and test strategies to address possible future impacts.
In short, remain calm! This flyby is a good thing!
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.
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.
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!