Having studies countless asteroids in near-Earth space, astronomers have come to understand that the majority of these rocks fall into one of two categories: S-type (grey) and C-type (red). These are defined by the types of materials on their surfaces, with S-type asteroids being primarily composed of silicate rock and C-type asteroids being made up of carbon materials.
However, there is also what are known as blue asteroids, which make up only a fraction of all known Near-Earth Objects (NEO). But when an international team astronomers observed the blue asteroid (3200) Phaeton during a flyby of Earth, they spotted behavior that was more consistent with a blue comet. If true, then Phaeton is of a class of objects that are so rare, they are almost unheard of.
The OSIRIS-REx mission is an historic one, since it will be the first US spacecraft to conduct a sample-return mission with an asteroid. In the meantime, as the probe has makes its way further into space, it has been providing some truly breathtaking images of the journey. Consider the recently-released composite image of the Earth-Moon system, which NASA created using images that were taken by the probe on October 2nd, 2017.
The images were all taken by the probe’s MapCam instrument, a medium-range camera designed to capture images of outgassing around Bennu and help map its surface in color. On this occasion, it snapped three beautiful pictures of Earth and the Moon. These images were all taken when the spacecraft was at a distance of approximately 5 million km (3 million mi) from Earth – about 13 times the distance between the Earth and the Moon.
As part of the OSIRIS-REx Camera Suite (OCAMS), which is operated by researchers at the University of Arizona, the CapCam has four color filters. To produce the image, three of them (b, v and w) were used as a blue, green and red filters and then stacked on top of each other. The Earth and Moon were each color-corrected, and the Moon was brightened to make it more easily visible.
A second image of planet Earth (shown above), was taken on September 22nd, 2017, by one of the probe’s navigational cameras (NavCam 1). As the name suggests, this instrument is intended to help OSIRIS-REx orient itself while making its journey to Bennu and while it studies the asteroid. This is done by tracking starfields in space (while in transit) and landmarks on Bennu’s surface once it has arrived.
The image was taken when OSIRIS-REx was at a distance of 110,000 km (69,000 mi) from Earth. This was just after the probe had completed an Earth gravity-assist maneuver, where it used Earth’s gravitational force to slingshot around its equator and pick up more speed. The original image (shown below) was rotated so that the North Pole would be pointed up and the entire image was enlarged to provide more detail.
As you can see in the altered image, North America is visible on the upper right portion, while Hurricane Maria and the remnants of Hurricane Jose are visible in the far upper-right. The acquisition of these images was the result of painstaking calculations and planning, which were performed in advance by engineers and navigation specialists on the mission team using software called Systems Tool Kit (STK).
These plans were developed to ensure that the probe would be able to snap pictures with precise timing, which were then uploaded to the spacecraft’s computer weeks ahead of time. Within hours of the probe executing its gravity-assist maneuver, crews on the ground were treated to the first images from the spacecraft’s navigational cameras, which confirmed that the probe was following the right path.
The probe is scheduled to reach Bennu in December of 2018, with approach operations commencing this coming August. Bennu is also expected to make a close pass with Earth several centuries from now, and could even collide with us by then. But for the time being, it represents a major opportunity to study the history and evolution of the Solar System, since it is essentially a remnant left over from its formation.
By studying this asteroid up close, and bringing samples back to Earth for further study, the OSRIS-REx mission could help us understand how life began on Earth and where the Solar System as a whole is headed. But in the meantime, the probe has been able to provide us with some beautiful snapshots of Earth, which serve to remind us all of certain things.
Much like Voyager 1‘s “Pale Blue Dot” photo, seeing Earth from space helps to drive home the fact that life is rare and precious. It also reminds us that we, as a species, are all in this together and completely and utterly dependent on our planet and its ecosystems. Once in awhile, we need to be reminded of these things. Otherwise, we might do some stupid – like ruin it!
In April of 2016, astronomers became aware of a distant object that appeared to be orbiting the Sun, but was also passing close enough to Earth that it could be periodically viewed using the most powerful telescopes. Since then, there has been ample speculation as to what this “Temporary Moon” could be, with most astronomers claiming that it is likely nothing more than an asteroid.
However, some suggested that it was a burnt-out rocket booster trapped in a near-Earth orbit. But thanks to new study by a team from the University of Arizona’s Lunar and Planetary Laboratory, this object – known as (469219) 2016 HO3 – has been confirmed as an asteroid. While this small near-Earth-asteroid orbits the Sun, it also orbits Earth as a sort of “quasi-satellite”.
The team that made this discovery was led by Vishnu Reddy, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory. Their research was also made possible thanks to NASA’s Near-Earth Object Observations Program. This program is maintained by NASA’s Center for Near-Earth Object Studies (CNEOS) and provides grants to institutions dedicated to the research of NEOs.
The details of this discovery were presented this week at the 49th Annual Meeting of the Division for Planetary Sciences in Utah at a presentation titled “Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3”. During the course of the presentation, Reddy and his colleagues described how they spotted the object using the Large Binocular Telescope (LBT) at the LBT Observatory on Mount Graham in southeastern Arizona.
According to their observations, 2016 HO3 measures just 100 meters (330 feet) across and is the most stable quasi-satellite discovered to date (of which there have been five). Over the course of a few centuries, this asteroid remains at a distance of 38 to 100 lunar distances – i.e. the distance between the Earth and the Moon. As Reddy explained in a UANews press statement, this makes the asteroid a challenging target:
“While HO3 is close to the Earth, its small size – possibly not larger than 100 feet – makes it challenging target to study. Our observations show that HO3 rotates once every 28 minutes and is made of materials similar to asteroids.”
Discovering the true nature of this object has also solved another big question – namely, where did 2016 HO3 come from? For those speculating that it might be space junk, it then became necessary to determine what the likely source of that junk was. Was it a remnant of an Apollo-era mission, or something else entirely? By determining that it is actually an NEO, Reddy and his team have indicted that it likely comes from the same place as other NEOs.
Reddy and his colleagues also indicated that 2016 HO3 reflected light off its surface in a way that is similar to meteorites that have been studied here on Earth. This was another indication that 2016 HO3 has similar origins to other NEOs (some of which have entered our atmosphere as meteors) which are generally asteroids that were kicked out of the Main Belt by Jupiter’s gravity.
“In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 with the Large Binocular Telescope and the Discovery Channel Telescope,” Reddy said. “The derived rotation period and the spectrum of emitted light are not uncommon among small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs.”
But unlike other NEOs which periodically cross Earth’s orbit, “quasi-satellites” are distinguished by their rather unique orbits. In the case of 2016 HO3, it has an orbit that follows a similar path to that the Earth’s; but because it is not dominated by the Earth’s gravity, their two orbits are out of sync. This causes 2016 HO3 to make annual loops around the Earth as it orbits the Sun.
Christian Veillet, one of co-authors of the presentation, is also the director of the LBT Observatory. As he explained, this characteristic could make “quasi-satellites” ideal targets for future NEO studies:
“Of the near-Earth objects we know of, these types of objects would be the easiest to reach, so they could potentially make suitable targets for exploration. With its binocular arrangement of two 8.4-meter mirrors, coupled with a very efficient pair of imagers and spectrographs like MODS, LBT is ideally suited to the characterization of these Earth’s companions.”
Similarly, their orbital characteristic could make “quasi-satellites” an ideal target for future space missions. One of NASA’s main goals in the coming decade is to send a crewed mission to a Near-Earth Object in order to test the Orion spacecraft and the Space Launch System. Such a mission would also help develop the necessary expertise for mounting missions deeper into space (i.e. to Mars and beyond).
The study of Near-Earth Objects is also of immense importance when it comes to determining how and where as asteroid might pose a threat to Earth. This knowledge allows for advanced warnings which can potentially save lives. It is also significant when it comes to the development of proposed counter-measures, several of which are currently being explored.
And be sure to enjoy this video of 2016 HO3’s orbit, courtesy of NASA’s Jet Propulsion Laboratory:
Yesterday (on May 8th, 2017), an asteroid swung past Earth on its way towards the Sun. This Near Earth Object (NEO), known as 2017 HX4, measures between 10 and 33 meters (32.8 and 108 feet) and made its closest approach to Earth at 11:58 am UT (7:58 am EDT; 4:58 am PT). Naturally, there were surely those who wondered if this asteroid would hit us and trigger a terrible cataclysm!
But of course, like most NEOs that periodically make a close pass to Earth, 2017 HX4 passed us by at a very safe distance. In fact, the asteroid’s closest approach to Earth was estimated to be at a distance of 3.7 Lunar Distances (LD) – i.e. almost four times the distance between the Earth and the Moon. This, and other pertinent information was tweeted in advance by the International Astronomical Union’s Minor Planet Center (IAU MPC) on April 29th.
This object was first spotted on April 26th, 2017, using the 1.8 meter Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), located at the summit of Haleakala in Hawaii. Since that time, it has been monitored by multiple telescopes around the world, and its tracking data and information about its orbit and other characteristics has been provided by the IAU MPC.
With funding provided by NASA’s Near-Earth Object Observations program, the IAU MPC maintains a centralized database that is responsible for the identification, designation and orbit computations of all the minor planets, comets and outer satellites of the Solar System. Since it’s inception, it has been maintaining information on 16,202 Near-Earth Objects, 729,626 Minor Planets, and 3,976 comets.
But it is the NEOs that are of particular interest, since they periodically make close approaches to Earth. In the case of 2017 HX4, the object has been shown to have an orbital period of 2.37 years, following a path that takes it from beyond the orbit of Venus to well beyond the orbit of Mars. In other words, it orbits our Sun at an average distance (semi-major axis) of 1.776 AU, ranging from about 0.88 AU at perihelion to 2.669 AU at aphelion.
From these combined observations, the IAU MPC was able to compile information on the object’s orbital period, when it would cross Earth’s orbit, and just how close it would come to us in the process. So, as always, there was nothing to worry about here folks. These objects are always spotted before they cross Earth’s orbit, and their paths, periods and velocities and are known about in advance.
Even so, it’s worth noting that an object of this size was nowhere near to be large enough to cause an Extinction Level Event. In fact, the asteroid that struck Earth 65 millions year ago at the end of Cretaceous era – which created the Chicxulub Crater on the Yucatan Peninsula in Mexico and caused the extinction of the dinosaurs – was estimated to measure 10 km across.
At 10 to 33 meters (32.8 to 108 feet), this asteroid would certainly have caused considerable damage if it hit us. But the results would not exactly have been cataclysmic. Still, it might not be too soon to consider getting off this ball of rock. You know, before – as Hawking has warned – a single event is able to claim all of humanity in one fell swoop!
The MPC is currently tracking the 13 NEOs that were discovered during the month of May alone, and that’s just so far. Expect to hear more about rocks that might cross our path in the future.
Every year, the NASA Innovative Advanced Concepts (NIAC) program puts out the call to the general public, hoping to find better or entirely new aerospace architectures, systems, or mission ideas. As part of the Space Technology Mission Directorate, this program has been in operation since 1998, serving as a high-level entry point to entrepreneurs, innovators and researchers who want to contribute to human space exploration.
This year, thirteen concepts were chosen for Phase I of the NIAC program, ranging from reprogrammed microorganisms for Mars, a two-dimensional spacecraft that could de-orbit space debris, an analog rover for extreme environments, a robot that turn asteroids into spacecraft, and a next-generation exoplanet hunter. These proposals were awarded $100,000 each for a nine month period to assess the feasibility of their concept.
This simulation by Tom Ruen shows the trajectory of 2015 TB145 across the sky, showing tracer spheres spaced at one hour intervals along its path.
Halloween fireballs, a Supermoon and now a near-Earth asteroid flyby. What a week! While 2015 TB145 won’t be visible in binoculars because of its relative faintness and glare from a nearby waning gibbous Moon, you should be able to see it in an 8-inch telescope or larger telescope without too much difficulty.
Determined amateurs might even catch it in instruments as small as 4.5 inches especially tomorrow morning when the fleeing space mountain will brighten to around magnitude +10.
For western hemisphere observers, TB145 begins the evening in Orion’s Shield not far below the Hyades Cluster looking like a magnitude +11.5 star crawling northeast through the star field. By dawn on Halloween, it will top out around magnitude +10.2 as it zips through Taurus and Auriga traveling around 3-5° per hour depending on the time you look. For most of the night, TB145 will move swiftly enough to notice its motion in real time, resembling an Earth-orbiting satellite. Closest approach occurs around 17:00 UT (noon CDT) when it pass along bottom of the Big Dipper Bowl at around 10° hour. Amazing!
My hope is that these maps will help you spot and follow this zippy, aircraft carrier-sized boulder. Three of the four maps cover most of the time between 5:00 and 11:45 UT, equivalent to midnight CDT tonight to 6:45 a.m. tomorrow morning. I used the very latest orbital elements and hand plotted the positions (a tedious exercise but worth it!) at 15-minute intervals. For convenience, when you print them out, I’d suggest using a straight edge to draw a line connecting the position dots.
As we discussed in the previous Universe Today story, parallax comes into play when viewing any nearby Solar System object. Three of the maps show the asteroid’s position from the North Central U.S. One depicts the view from the South Central U.S. from 11-11:45 UT. Parallax is minor early on from midnight to 2 or 3 a.m. but becomes more significant near closest approach. This is based on comparisons I made between latitudes 47°-32° North.
I apologize for the limited number of maps in this article but hope these and the do-it-yourself approach described in the earlier article will be enough to set you on TB145’s trail.
As always when trying to spot asteroids on the move, pick a time and camp out at that spot with your telescope five minutes before the expected arrival time. Take the time to casually memorize the star patterns, so when the interloper arrives, you’ll pick it out straightaway. Again, depending on your location both east-west and north-south of the paths charted, TB145 may arrive a couple minutes earlier or later, but once you spot it, hold on tight. You’ll be going on a most exciting ride!
We’d love to hear from you whether or not you were successful seeing it. If the weather’s uncooperative or you don’t have a telescope, Gianluca Masi’s got your back. He’ll webcast the flyby live on his Virtual Telescope site starting at 7 p.m. CDT (0:00 UT) tonight Oct. 30-31.
Now let’s see the flyby of Earth from the asteroid’s point of view, also by Tom Ruen. Enjoy!
Trick or treat! I think we’re definitely in for a treat. 2015 TB145 will fly past Earth at a safe distance slightly farther than the moon’s orbit on Oct. 31 at 12:05 p.m. CDT (17:05 UT). Estimated at 1,300 feet (400-meters) across, this Great Pumpkin of an asteroid will be big enough and close enough to show in small telescopes.
The close approach of such of TB145 will make for great science opportunities, too. Several optical observatories and the radar capabilities of the agency’s Deep Space Network at Goldstone, California will be tracking this flying mountain as will many amateur astronomers. The 110-foot (34-meter) Goldstone antenna will ping the asteroid with radio waves; the returning echoes will be collected by dishes in West Virginia and Puerto Rico and used to construct images showing the object’s surface features, shape and dimensions. NASA scientists hope to obtain radar images of the asteroid as fine as about 7 feet (2 meters) per pixel.
“The close approach of 2015 TB145 at about 1.3 times the distance of the moon’s orbit, coupled with its size, suggests it will be one of the best asteroids for radar imaging we’ll see for several years,” said Lance Benner, of JPL, who leads NASA’s asteroid radar research program. “We plan to test a new capability to obtain radar images with two-meter resolution for the first time and hope to see unprecedented levels of detail.”
Astronomers first nabbed asteroid 2015 TB145 on Oct. 10, 2015, using the University of Hawaii’s Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) telescope atop Mt. Haleakala in Maui. According to the catalog of near-Earth objectskept by the Minor Planet Center, this is the closest currently known approach by an object this large until asteroid 1999 AN10 (about 2,600 feet or 800-m in size) zips by at about 1 lunar distance in August 2027.
The gravitational influence of the asteroid is so small it will have no detectable effect on the Moon or anything here on Earth, including our planet’s tides or tectonic plates. But the planet will certainly have an effect on the asteroid. Earth’s gravity will deflect TB145’s path during the close approach, making it tricky this far out to create an accurate map of its flight across the sky. That’s why the two maps I’ve included with this article are only approximate. As we get closer to Halloween, further refinements in the asteroid’s orbit will allow for more accurate path-making.
Because the asteroid passes so near Earth, parallax will shift its path north or south up to 1/2°. Parallax is the apparent shift in an object’s position against the more distant background stars depending on the observer’s location on Earth. You can see how parallax works using your eyes and a finger. Stick your arm straight out in front of you and hold up your index finger. Open and close your right and then your left eye in a back and forth blinking pattern and watch your finger jump back and forth across the more distant background. Each eye sees the thumb from a slightly different perspective, causing it to shift position against the distant scene.
This happens all the time with the Moon. You might see it conjunct with a bright planet where skywatchers on the opposite side of the planet see an occultation. That’s why it’s best to make your own map of TB145’s wild ride across the sky. When closest to Earth, the asteroid will cover a Full Moon diameter about every 3 minutes as it tears by us at 22 miles per second (35 km/sec). Without a good map, it’ll get away from you.
Method #1: Using Stellarium
Download the free sky-plotting program Stellarium. Once you’ve set your location, either hit F2 or click on the Configuration icon in the lower left corner of your screen. Now select the Plugins tab then Solar System Editor. Click on Configure at the bottom of the tab, choose Solar System and click Import orbital elements in MPC format.
Next, select the Asteroids option and then from the bookmarks list, choose MPCORB: near-Earth asteroids (NEAs) and then Get orbital elements. Allow the list — a very large one — to load then scroll through it until you find 2015 TD145 and put a check mark in the box. Then click Add objects.
Still with me? OK, close the Solar System editor and press F3 or select the magnifying glass icon in the lower left corner of your screen, then type in the asteroid’s name exactly as 2015 TD145. Hit enter and you’ll see a set of rotating red crosshairs. Bingo! This where the asteroid will be at the time you chose. You can adjust your magnitude range, field of view and even download additional files of fainter stars and deep sky objects. Unfortunately, Stellarium can’t draw an arc showing TB145’s changing position with time. Cross your fingers that appears in the next iteration.
Method #2: Download up-to-date orbital elements into your sky-charting program
Let’s say you already have a sky-charting program like Guide, Dance of the Planets, MegaStar or Starry Night. Go to the Minor Planet &Comet Ephemeris Serviceand type in 2015 TB145 in the big, blank box. Next, scroll down and select your program from the list and click on Get Ephemerides/HTML page. Save the file of orbital elements that pops up and place into the appropriate folder in your program. Open your program, select 2015 TB145 and make a chart!
Method #3: Manually input orbital elements into your program
You can also go to JPL’s Horizons site for the very latest orbital elements you can manually input in your program. 2015 TB145 is expected to be as bright as magnitude +10.1 (no problem in a 4.5-inch scope) but that occurs during the afternoon for the Americas. The Middle East and Asia are the place to be for closest approach. Peak brightness over the U.S. will occur before dawn on Halloween, so you can begin observation around 11 p.m. local time Friday evening October 30 when Orion comes up in the east. The asteroid starts shines at around magnitude +11-11.5 that evening and brightens overnight to around +10.3-10.5 before dawn for the Americas.
A word about tracking fast-moving asteroids. I’ve found that the best way to catch sight of one is to “camp” at the place they’ll pass at a certain time. Say you want to see TB145 at 1:15 a.m. October 31. Make a chart that shows its position every 15 minutes. Five minutes before it arrives at the 1:15 a.m. spot, point your telescope there and wait for a “moving star” to enter the field of view. If you don’t see it right way, wait a few minutes and pan around to the north and south of the location. By the way, the asteroid will pass less than a degree northwest of the Crab Nebula (M1) in Taurus around 10:30 UT (5:30 a.m. CDT).
Be aware that the bright, waning gibbous Moon will be within 10° of the asteroid when it’s best visible in the Americas. While this will make observing the asteroid more challenging, don’t let it stop you from trying. If bad weather gets in the way, Gianluca Masi has you covered. He’ll live-stream the flyby on his Virtual Telescope sitebeginning at 0:00 UT (7 p.m CDT) on October 31st.
One way or another, we’ll all have a shot at seeing the Great Pumpkin asteroid this Halloween.
UPDATE Oct. 27, 2015: There’s been some discussion about TB145’s orbit resembling that of a comet along with speculation it might be a dead or dormant comet. Amateur and professional astronomers have been watching it closely, looking for hints of activity such as a fuzzy coma. So far, photos show the asteroid as completely stellar.
I also wanted to update you on its visibility. Those with 10-inch or larger telescopes can begin looking for the object Thursday night Oct. 29th when it reaches magnitude +13.5. The following night it leaps to +11.5 with a peak brightness of +10.0 occurring around 14:00 UT (9 a.m. CDT) on Halloween. TB145 fades rapidly thereafter – down to 15th magnitude just 8 hours later.
A lot of asteroids pass near Earth every year. Many are the size of a house, make close flybys and zoom out of the headlines. 2004 BL86 is a bit different. On Monday evening January 26th, it will become the largest asteroid to pass closest to Earth until 2027 when 1999 AN10 will approach within one lunar distance.
Big is good. 2004 BL86 checks in at 2,230 feet (680-m) wide or nearly half a mile. Add up its significant size and relatively close approach – 745,000 miles (1.2 million km) – and something wonderful happens. This newsy space rock is expected to reach magnitude +9.0, bright enough to see in a 3-inch telescope or even large binoculars.
This is a rare opportunity then to see an Earth-approaching asteroid so easily. All you need is a good map as 2004 BL86 will be zipping along at two arc seconds per second or two degrees (four Moon diameters) per hour. That means you’ll see it move in real time like a slow satellite inching its way across the sky. Cool!
As you can see from its name, 2004 BL86 was discovered 11 years ago in 2004 by the Lincoln Near-Earth Asteroid Research (LINEAR), an MIT Lincoln Laboratory program to track near-Earth objects funded by the U.S. Air Force and NASA. As of September 15, 2011, the search has swept up 2,423 new asteroids and 279 new comets.
All asteroids with well-known orbits receive a number. The first asteroid, 1 Ceres, was discovered in 1801. The 4,150th asteroid, 4150 Starr and named for the Beatles’ Ringo Starr, was found in 1984. 2004 BL86 will likely be the highest-numbered asteroid any of us will ever see. How does 357,439 sound to you?
Observers in the Americas, Europe and Africa will have the best seats for viewing the asteroid, which will shine brightest between 7 p.m. and midnight CST from a comfortably high perch in Cancer the Crab not far from Jupiter. The half-moon will also be out but over in the western sky, so shouldn’t get in the way of seeing our speedy celeb.
Not only will 2004 BL86 pass near a few fairly bright stars but the Beehive Cluster (M44) will temporarily gain a new member between 11 p.m. and midnight as the asteroid buzzes across the well-known star cluster.
“Monday, January 26 will be the closest asteroid 2004 BL86 will get to Earth for at least the next 200 years,” said Don Yeomans, who’s retiring as manager of NASA’s Near Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California, after 16 years in the position.
To learn more about the space rock and acquire close-ups of its surface, NASA’s Deep Space Network antenna at Goldstone, California, and the Arecibo Observatory in Puerto Rico will attempt to ping the asteroid with microwaves to create radar-generated images of the asteroid during the days surrounding its closest approach to Earth.
“When we get our radar data back the day after the flyby, we will have the first detailed images,” said radar astronomer Lance Benner of JPL, principal investigator for the Goldstone radar observations of the asteroid. “At present, we know almost nothing about the asteroid, so there are bound to be surprises.”
While 2004 BL86 will be brightest Monday night, that’s not the only time amateur astronomers might see it. It comes into view for southern hemisphere observers around magnitude +13 on Jan. 24 and leaves the scene at a similar brightness high in the northeastern sky in the northern hemisphere on the 29th. If you use a star-charting program like Starry Night, Guide, MegaStar and others, you can get updated orbital element packages HERE. Just select your program and download the Observable Unusual Minor Planets file. Open it in your software and create maps for the entire apparition.
One last observing tip before you go your own way. Close asteroids will sometimes be a little bit off a particular track depending on your location. Not much but enough that I recommend you scan not just the single spot where you expect to see it but also nearby in the field of view. If you see a “star” on the move – that’s it.
As always, Dr. Gianluca Masi, Italian astrophysicist, will share his live coverage of the eventbeginning at 1:30 p.m. (19:30 UT) Jan. 26th.
Let us know if you see our not-so-little cosmic friend. Good luck!
How hazardous are the thousands and millions of asteroids that surround the third rock from the Sun – Earth? Since an asteroid impact represents a real risk to life and property, this is a question that has been begging for answers for decades. But now, scientists at NASA’s Jet Propulsion Laboratory have received data from a variety of US Department of Defense assets and plotted a startling set of data spanning 20 years.
This latest compilation of data underscores how frequent some of these larger fireballs are, with the largest being the Chelyabinsk event on February 15, 2013 which injured thousands in Russia. The new data will improve our understanding of the frequency and presence of small and large asteroids that are hazards to populated areas anywhere on Earth.
The data from “government sensors” – meaning “early warning” satellites to monitor missile launches (from potential enemies) as well as infrasound ground monitors – shows the distribution of bolide (fireball) events. The data first shows how uniformly distributed the events are around the world. This data is now released to the public and researchers for more detailed analysis.
The newest data released by the US government shows both how frequent bolides are and also how effectively the Earth’s atmosphere protects the surface. A subset of this data had been analyzed and reported by Dr. Peter Brown from the University of Western Ontario, Canada and his team in 2013 but included only 58 events. This new data set holds 556 events.
The newly released data also shows how the Earth’s atmosphere is a superior barrier that prevents small asteroids’ penetration and impact onto the Earth’s surface. Even the 20 meter (65 ft) Chelyabinsk asteroid exploded mid-air, dissipating the power of a nuclear blast 29.7 km (18.4 miles, 97,400 feet) above the surface. Otherwise, this asteroid could have obliterated much of a modern city; Chelyabinsk was also saved due to sheer luck – the asteroid entered at a shallow angle leading to its demise; more steeply, and it would have exploded much closer to the surface. While many do explode in the upper atmosphere, a broad strewn field of small fragments often occurs. In historical times, towns and villages have reported being pelted by such sprays of stones from the sky.
NASA and JPL emphasized that investment in early detection of asteroids has increased 10 fold in the last 5 years. Researchers such as Dr. Jenniskens at the SETI Institute has developed a network of all-sky cameras that have determined the orbits of over 175,000 meteors that burned up in the atmosphere. And the B612 Foundation has been the strongest advocate of discovering of all hazardous asteroids. B612, led by former astronauts Ed Lu and Rusty Schweikert has designed a space telescope called Sentinel which would find hazardous asteroids and help safeguard Earth for centuries into the future.
Speed is everything. While Chelyabinsk had just 1/10th the mass of Nimitz-class super carrier, it traveled 1000 times faster. Its kinetic energy on account of its speed was 20 to 30 times that released by the nuclear weapons used to end the war against Japan – about 320 to 480 kilotons of TNT. Briefly, asteroids are considered to be any space rock larger than 1 meter and those smaller are called meteoroids.
Two earlier surveys can be compared to this new data. One by Eugene Shoemaker in the 1960s and another by Dr. Brown. The initial work by Shoemaker using lunar crater counts and the more recent work of Dr. Brown’s group, utilizing sensors of the Department of Defense, determined estimates of the frequency of asteroid impacts (bolide) rates versus the size of the small bodies. Those two surveys differ by a factor of ten, that is, where Shoemaker’s shows frequencies on the order of 10s or 100s years, Brown’s is on the order of 100s and 1000s of years. The most recent data, which has adjusted Brown’s earlier work is now raising the frequency of hazardous events to that of the work of Shoemaker.
The work of Dr. Brown and co-investigators led to the following graph showing the frequency of collisions with the Earth of asteroids of various sizes. This plot from a Letter to Nature by P. Brown et al. used 58 bolides from data accumulated from 1994 to 2014 from government sensors. Brown and others will improve their analysis with this more detailed dataset. The plot shows that a Chelyabinsk type event can be expected approximately every 30 years though the uncertainty is high. The new data may reduce this uncertainty. Tungunska events which could destroy a metropolitan area the size of Washington DC occur less frequently – about once a century.
Asteroids come in all sizes. Smaller asteroids are much more common, larger ones less so. A common distribution seen in nature is represented by a bell curve or “normal” distribution. Fortunately the bigger asteroids number in the hundreds while the small “city busters” count in the 100s of thousands, if not millions. And fortunately, the Earth is small in proportion to the volume of space even just the space occupied by our Solar System. Additionally, 69% of the Earth’s surface is covered by Oceans. Humans huddle on only about 10% of the surface area of the Earth. This reduces the chances of any asteroid impact effecting a populated area by a factor of ten.
Altogether the risk from asteroids is very real as the Chelyabinsk event underscored. Since the time of Tugunska impact in Siberia in 1908, the human population has quadrupled. The number of cities of over 1 million has increased from 12 to 400. Realizing how many and how frequent these asteroid impacts occur plus the growth of the human population in the last one hundred years raises the urgency for a near-Earth asteroid discovery telescope such as B612’s Sentinel which could find all hazardous objects in less than 10 years whereas ground-based observations will take 100 years or more.
The estimated cumulative flux of impactors at the Earth. The bolide impactor flux at Earth (Bolide flux 1994-2013 – black circles) based on ~20 years of global observations from US Government sensors and infrasound airwave data. Global coverage averages 80% among a total of 58 observed bolides with E > 1 kt and includes the Chelyabinsk Chelyabinsk bolide (far right black circle). This coverage correction is approximate and the bolide flux curve is likely a lower limit. The brown-coloured line represents an earlier powerlaw fit from a smaller dataset for bolides between 1 – 8 m in diameter15. Error bars represent counting statistics only. For comparison, we plot de-biased estimates of the near-Earth asteroid impact frequency based on all asteroid survey telescopic search data through mid- 2012 (green squares)8 and other earlier independently analysed telescopic datasets including NEAT discoveries (pink squares) and finally from the Spacewatch (blue squares) survey, where diameters are determined assuming an albedo of 0.1. Energy for telescopic data is computed assuming a mean bulk density of 3000 kgm-3 and average impact velocity of 20.3 kms-1. The intrinsic impact frequency for these telescopic data was found using an average probability of impact for NEAs as 2×10-9 per year for the entire population. Lunar crater counts converted to equivalent impactor flux and assuming a geometric albedo of 0.25 (grey solid line) are shown for comparison9, though we note that contamination by secondary craters and modern estimates of the NEA population which suggest lower albedos will tend to shift this curve to the right and down. Finally, we show estimated influx from global airwave measurements conducted from 1960-1974 which detected larger (5-20m) bolide impactors (upward red triangles) using an improved method for energy estimation compared to earlier interpretations of these same data.
What a roller coaster week it’s been. If partial eclipses and giant sunspots aren’t your thing, how about a close flyby of an Earth-approaching asteroid? 2014 SC324 was discovered on September 30 this year by the Mt. Lemmon Surveyhigh in the Catalina Mountains north of Tucson, Arizona. Based on brightness, the tumbling rock’s size is estimated at around 197 feet (60-m), on the large side compared to the many small asteroids that whip harmlessly by Earth each year.
Closest approach happens around 2 p.m. CDT (7 p.m. UT) Friday afternoon when our fast friend misses Earth by just 351,000 miles (565,000 km) or 1.5 times the distance to the Moon. This is a very safe distance, so we can finish up our lunches without a jot of concern. But the asteroid’s combination of size and proximity means amateur astronomers with a 10-inch or larger telescope will be able to track it across the sky beginning tonight (Oct. 23) and continuing through tomorrow night. 2014 SC324 should shine tolerably bright this evening at around magnitude +13.5.
Bright here is something of a euphemism, but when it comes to new Earth-approaching asteroids, this is within range of many amateur instruments. And because 2014 SC324 is “only” a half million miles away tonight, it’s not moving so fast that you can’t plot its arc on a single star chart, spot it and go for a ride.
Simulation based on recent data showing the known asteroids orbiting the Sun
By Friday evening, the new visitor will have faded a bit to magnitude +14. You can create a track for 2014 SC324 by inputting its orbital elements into a variety of astro software programs like MegaStar, the Sky, and Le Ciel. Elements are available via the Minor Planet Center and Horizons. Once saved, the program will make a track of the asteroid’s movement at selected time intervals. Print out the chart and you’re ready for the hunt!
You can also go to Horizons, ask for a list of positions every 15 minutes for example and then hand plot those positions in right ascension (R.A.) and declination (Dec.) on a star map. This is what I do. I find the the general chunk of sky the asteroid’s passing through, print the map and then mark positions in pencil and connect them all with a line. Now I’ve got a chart I can use at the telescope based on the most current orbit.
Tonight the errant mountain will rumble through Aries the Ram, which is conveniently located in the eastern sky below Andromeda and the Great Square of Pegasus at nightfall.
Finding a dim, fast-moving object is doubtless an exciting challenge, but if you lack the equipment or the weather doesn’t cooperate, you can see the show online courtesy of Italian astrophysicist Gianluca Masi. He’ll stream the close encounter live on his Virtual Telescope Project website beginning at 7 p.m. CDT (midnight UT) tomorrow night October 24-25.