This animation, created from individual radar images, clearly show the rough outline of 2004 BL86 and its newly-discovered moon. Credit: NASA/JPL-Caltech
Wonderful news! Asteroid 2004 BL86, which passed closest to Earth today at a distance of 750,000 miles (1.2 million km), has a companion moon. Scientists working with NASA’s 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, California, have released the first radar images of the asteroid which show the tiny object in orbit about the main body.
While these are the first images of it, the “signature” of the satellite was seen in light curve data reported earlier by Joseph Pollock (Appalachian State University, North Carolina) and Petr Prave (Ondrejov Observatory, Czech Republic) according to Lance Bennerwho works with the radar team at Goldstone.
2004 BL86 measures about 1,100 feet (325 meters) across while its moon is approximately 230 feet (70 meters) across. The asteroid made its closest approach today (Jan. 26th) at 10:19 a.m. (CST), however it will peak in brightness this evening around 10 p.m. (4:00 UT) at magnitude +9.0. Unlike some flybys, 2004 BL86 will remain within a few tenths of a magnitude of peak brightness from 6 p.m. tonight (CST) through early tomorrow morning, so don’t miss the chance to see it in your telescope.
Don’t expect to see the diminutive moon visually – the entire system will only appear as a point of light, but I’m sure you’ll agree it’s cool just knowing it’s there.
The double asteroid (90) Antiope and its companion S/2000 (90) 1. The two objects are separated by 106 miles (171 km), and they perform their celestial dance in 16.5 hours. The adaptive optics observations couldn’t resolve the shape of the individual components as they are too small. Credit: ESO
Among near-Earth asteroids, about 16% that are about 655 feet (200 meters) or larger are either binary or triple systems. While that’s not what you’d call common, it’s not unusual either. To date, we know of 240 asteroids with a single moon, 10 triple systems and the sextuple system of Pluto (I realize that’s stretching a bit, since Pluto’s a dwarf planet) – 268 companions total. 52 of those are near-Earth asteroids.
With a resolution of 13 feet (4-meters) per pixel we can at least see the roughness of the the main body’s surface and perhaps imagine craters there. No details are visible on the moon though it does appear elongated. I’m surprised how round the main body is given its small size. An object that tiny doesn’t normally have the gravity required to crush itself into a sphere. Yet another fascinating detail needing our attention.
Of course the main asteroid will get your attention tonight. Please check out our earlier story on 2004 BL86 which includes more details as well as charts to help you track it as it flies across Cancer the Crab tonight. This is the best view we’re going to get of it for the next two centuries.
Animation of Ceres made from Dawn images acquired on Jan. 13, 2015 (Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI)
Just sit back and watch the world turn… or should I say, watch the dwarf planet turn in this fascinating animation from Dawn as the spacecraft continues on its ion-powered approach to Ceres!
The images were captured by Dawn’s framing camera over the course on an hour on Jan. 13 at a distance of 238,000 miles (383,000 km) from Ceres. At 590 miles (950 km) wide Ceres is the largest object in the main asteroid belt.
“Already, the [latest] images hint at first surface structures such as craters,” said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research in Gottingen, Germany. “We have identified all of the features seen by Hubble on the side of Ceres we have observed, and there are also suggestions of remarkable structures awaiting us as we move even closer.”
Although these latest 27-pixel images from Dawn aren’t quite yet better than Hubble’s images from Jan. 2004, very soon they will be.
Comparison of HST and Dawn FC images of Ceres taken nearly 11 years apart
“The team is very excited to examine the surface of Ceres in never-before-seen detail,” said Chris Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles. “We look forward to the surprises this mysterious world may bring.”
Launched Sept. 27, 2007, Dawn previously spent over 13 months in orbit around the asteroid/protoplanet Vesta from 2011–12 and is now on final approach to Ceres. On March 6 Dawn will arrive at Ceres, becoming the first spacecraft to enter orbit around two different target worlds.
Artist view of an asteroid passing Earth. Credit: ESA/P.Carril
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 graphic depicts the passage of asteroid 2004 BL86, which will safely pass by the Earth on January 26th. Closest approach occurs around 10 a.m (CST) that day. The asteroid is currently only visible by astronomers with large telescopes who are located in the southern hemisphere. But by Jan. 26, the space rock’s changing position will make it visible to those in the northern hemisphere. Click to see an animation. Credit: NASA/JPL-Caltech
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.
Map showing the hourly progress of 2004 BL86 Monday evening January 26th as it treks across Cancer the Crab not far from Jupiter. Stars are shown to magnitude +9. Numbers at the tick marks show the time (CST) each hour starting at 6 p.m., then 7 p.m., 8 p.m. and so on. Click for a larger version. Created with Chris Marriott’s SkyMap program
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?
Some observers prefer a black on white map for tracking asteroids and deep sky objects. Click to view a larger version. Created with Chris Marriott’s SkyMap program
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.
More detailed map showing the hourly position of the asteroid through central Cancer. Stars plotted to magnitude +9.5. Click to get a larger version. Created with Chris Marriott’s SkyMap software
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.”
NASA’s Deep Space Network will be watching during 2004 BL86’s flyby Monday Jan. 26. Credit: NASA
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!
The idea that Mars could have supported life at one time is the subject of ongoing debate. Image credit: NASA
Mars is currently home to a small army robotic rovers, satellites and orbiters, all of which are busy at work trying to unravel the deeper mysteries of Earth’s neighbor. These include whether or not the planet ever had liquid water on its surface, what the atmosphere once looked like, and – most importantly of all – if it ever supported life.
And while much has been learned about Martian water and its atmosphere, the all-important question of life remains unanswered. Until such time as organic molecules – considered to be the holy grail for missions like Curiosity – are found, scientists must look elsewhere to find evidence of Martian life.
According to a recent paper submitted by an international team of scientists, that evidence may have arrived on Earth three and a half years ago aboard a meteorite that fell in the Moroccan desert. Believed to have broken away from Mars 700,000 years ago, so-called Tissint meteorite has internal features that researchers say appear to be organic materials.
The paper appeared in the scientific journal Meteoritics and Planetary Sciences. In it, the research team – which includes scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) – indicate organic carbon is located inside fissures in the rock. All indications are the meteorite is Martian in origin.
“So far, there is no other theory that we find more compelling,” says Philippe Gillet, director of EPFL’s Earth and Planetary Sciences Laboratory. He and his colleagues from China, Japan and Germany performed a detailed analysis of organic carbon traces from a Martian meteorite, and have concluded that they have a very probable biological origin.
Artist’s conception of an fragment as it blasts off from Mars as a result of a meteor impact. Credit: The Planetary Society
The scientists argue that carbon could have been deposited into the fissures of the rock when it was still on Mars by the infiltration of fluid that was rich in organic matter.
If this sounds familiar, you may recall a previous Martian meteorite named ALH84001, found in the Allen Hills region in Antarctica. In 1996 NASA researchers announced they had found evidence within ALH84001 that strongly suggested primitive life may have existed on Mars more than 3.6 billion years ago. While subsequent studies of the now famous Allen Hills Meteorite shot down theories that the Mars rock held fossilized alien life, both sides continue to debate the issue.
This new research on the Tissint meteorite will likely be reviewed and rebutted, as well.
The researchers say the meteorite was likely ejected from Mars after an asteroid crashed on its surface, and fell to Earth on July 18, 2011, and fell in Morocco in view of several eyewitnesses.
Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Several research teams have already shown that this component is organic in nature, but they are still debating where the carbon came from.
Chemical, microscopic and isotope analysis of the carbon material led the researchers to several possible explanations of its origin. They established characteristics that unequivocally excluded a terrestrial origin, and showed that the carbon content were deposited in the Tissint’s fissures before it left Mars.
This research challenges research proposed in 2012 that asserted that the carbon traces originated through the high-temperature crystallization of magma. According to the new study, a more likely explanation is that liquids containing organic compounds of biological origin infiltrated Tissint’s “mother” rock at low temperatures, near the Martian surface.
A piece of the Tissint meteorite that landed on Earth on July 18th, 2011. Credit: EPFL/Alain Herzog
These conclusions are supported by several intrinsic properties of the meteorite’s carbon, e.g. its ratio of carbon-13 to carbon-12. This was found to be significantly lower than the ratio of carbon-13 in the CO2 of Mars’s atmosphere, previously measured by the Phoenix and Curiosity rovers.
Moreover, the difference between these ratios corresponds perfectly with what is observed on Earth between a piece of coal – which is biological in origin – and the carbon in the atmosphere.
The researchers note that this organic matter could also have been brought to Mars when very primitive meteorites – carbonated chondrites – fell on it. However, they consider this scenario unlikely because such meteorites contain very low concentrations of organic matter.
“Insisting on certainty is unwise, particularly on such a sensitive topic,” warns Gillet. “I’m completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars – at least in the past.”
Be sure to check out these videos from EPFL News, which include an interview with Philippe Gillet, EPFL and co-author of the study:
And this video explaining the history of the Tissint meteor:
A 3-D model of 6 Hebe based on its light curve. The asteroid is about 120 miles in diameter and orbits in the main asteroid belt between Mars and Jupiter. Credit: Charles University_Josef Durech_Vojtech Sidorin
In the reeds that line the banks of the celestial river Eridanus, you’ll find Hebe on the prowl this month. Discovered in 1847 by German amateur astronomer Karl Ludwig Hencke , the asteroid may hold the key to the origin of the H-chondrites, a large class of metal-rich stony meteorites found in numerous amateur and professional collections around the world. You can now see this interesting minor planet with nothing more than a pair of binoculars or small telescope.
Judging by his demeanor, it might have been unwise to tell Karl Hencke he was wasting his time looking for asteroids.
The first four asteroids – Ceres, Pallas, Juno and Vesta – were discovered in quick succession from 1801 to 1807. Then nothing turned up for years. Most astronomers wrongly assumed all the asteroids had been found and moved on to other projects like measuring the orbits of double stars and determining stellar parallaxes. Nothing could have been further from the truth. Hencke, who worked as a postmaster during the day, doggedly persisted in sieving the stars for new asteroids in his free time at night. His systematic search began in 1830. Fifteen years and hundreds of cold nights at the eyepiece later he turned up 5 Astrae (asteroid no. 5) on Dec. 8, 1845, and 6 Hebe on July 1, 1847.
Hebe orbits in the main asteroid belt between Mars and Jupiter with an average distance from the Sun of 225 million miles. It spins on its axis once every 7.3 hours. Credit: Wikipedia
Energized by the finds, astronomers returned to their telescopes with renewed gusto to join in the hunt once again. The rest is history. As of November 2014 there are 415,688 numbered asteroids and a nearly equal number of unnumbered discoveries. Fittingly, asteroid 2005 Hencke honors the man who kept the fire burning.
You’ll find Hebe trucking along in Eridanus this month just north of Delta (left) and Epsilon Eridani, a pair of +3.5 magnitude stars. This map shows stars to magnitude +9.5 with Hebe’s position marked every 5 nights. Click to enlarge. Source: Chris Marriott’s SkyMap software
At 120 miles (190 km) across, Hebe is one of the bigger asteroids (officially 33rd in size in the main belt) and orbits the Sun once every 3.8 years. It will be our guest this final month of the year shining at magnitude +8.2 in early December, +8.5 by mid-month and +8.9 when you don your party hat on New Year’s Eve. All the while, Hebe will loop across the barrens of Eridanus west of Orion. Use the maps here to help track it down. I’ve included a detailed color map above, but also created a “black stars on white” version for those that find reverse charts easier to use.
Use this wide view of the sky to get oriented before zeroing in with the more detailed map above. Hebe lies just a few degrees north of Delta and Epsilon Eridani for much of December. Best viewing time is from 10 p.m. to 2 a.m. local time early in the month. Source: Stellarium
In more recent times, Hebe’s story takes an interesting turn. Through a study of its gravitational nudges on other asteroids, astronomers discovered that Hebe is a very compact, rocky object, not a loosey-goosey pile of rubble like some asteroids. Its high density provides strong evidence for a composition of both rock and iron. Scientists can determine the approximate composition of an asteroid’s surface by studying its reflectance spectrum, or what colors or wavelengths are reflected back from the object after a portion is absorbed by its surface. They use infrared light because different minerals absorb different wavelengths of infrared light. That data is compared to infrared absorptions from rocks and meteorites found on Earth. Turns out, our friend Hebe’s spectrum is a good match to two classes of meteorites – the H-chondrites, which comprise 40% of known meteorites – and the rarer IIE silicated iron meteorites.
Did this slice of meteorite come from Hebe? A 12.9-gram specimen of NWA 2710, an H5 stony chondrite, sparkles in the light. The shiny flecks are iron-nickel metal set in a stony matrix. Credit: Bob King
Because Hebe orbits close to an unstable zone in the asteroid belt, any impacts it suffers are soon perturbed by Jupiter’s gravity and launched into trajectories than can include the Earth. When you spot Hebe in your binoculars the next clear night, you might just be seeing where many of the more common space rocks in our collections originated.
Artist view of an asteroid (with companion) passing near Earth. Credit: P. Carril / ESA
Asteroids and comets have a few things in common. They are both celestial bodies orbiting our Sun, and they both can have unusual orbits, sometimes straying close to Earth or the other planets. They are both “leftovers” — made from materials from the formation of our Solar System 4.5 billion years ago. But there are a few notable differences between these two objects, as well. The biggest difference between comets and asteroids, however, is what they are made of.
While asteroids consist of metals and rocky material, comets are made up of ice, dust, rocky materials and organic compounds. When comets get closer to the Sun, they lose material with each orbit because some of their ice melts and vaporizes. Asteroids typically remain solid, even when near the Sun.
Right now, the majority of asteroids reside in the asteroid belt, a region between the orbits of Mars and Jupiter which may hold millions of space rocks of varying sizes. On the other hand, the majority of comets are in the farthest reaches of our Solar System: either 1. in the Kuiper Belt — a region just outside the orbit of the dwarf planet Pluto that may have millions of icy comets (as well as many icy dwarf planets like Pluto and Eris); or 2. the Oort Cloud, a region where trillions of comets may circle the Sun at huge distances of up to 20 trillion kilometers (13 trillion miles).
Anillustration of what the Oort cloud might be like. Credit: Don Yeomans/JPL.
Some scientists think asteroids formed much closer to the Sun, where it was too warm for any ices to remain solid, while comets formed farther from the Sun and were therefore able to retain ice. However, other scientists think that the comets that are now in the Kuiper Belt and Oort cloud actually formed in the inner Solar System, but were then flung out from the gravitation effects of the giant planets Jupiter and Saturn.
We do know that gravitational perturbations periodically jar both asteroids and comets from their usual “homes” — setting them on orbital courses that bring them closer to the Sun, as well as Earth.
When comets approach the Sun, some of their ices melt. This causes another notable difference between asteroids and comets: comets have “tails” while asteroids generally don’t. When the ices in comets begin to melt and other materials vaporize from the heat from the Sun, this forms a glowing halo that extends outward from the comet as it sails through space. The ice and compounds like methane and ammonia develop a fuzzy, cloud-like shell called a coma. Forces exerted on the coma by the Sun’s radiation pressure and solar wind cause an enormous, elongated tail to form. Tails always points away from the Sun.
Asteroids typically don’t have tails, even those near the Sun. But recently, astronomers have seen some asteroids that have sprouted tails, such as asteroid P/2010 A2. This seems to happen when the asteroid has been hit or pummeled by other asteroids and dust or gas is ejected from their surfaces, creating a sporadic tail effect. These so-called “active asteroids” are a newly recognized phenomenon, and as of this writing, only 13 known active asteroids have been found in the main asteroid belt, and so they are very rare.
Another difference between asteroids and comets is in their orbital patterns. Asteroids tend to have shorter, more circular orbits. Comets tend to have very extended and elongated orbits, which often exceed 50,000 AU from the Sun. (*Note: 1 AU, or Astronomical Unit, equals the distance from the Earth to the Sun.) Some, called long-period comets come from the Oort Cloud and are in big elliptical orbits of the Sun that take them far out beyond the planets and back. Others, called short-period comets come from the Kuiper Belt and travel in shorter orbits around the Sun.
There is a big difference when it comes to numbers… although there is a caveat in that we don’t know precisely how many asteroids OR comets there are in our Solar System, since many have never been seen. Astronomers have discovered millions of asteroids – some as small as dust particles and others measuring hundreds of kilometers across. But as of this writing, astronomers have found only about 4,000 comets. However, some estimates say there could be one hundred billion comets in the Oort cloud.
The fact that asteroids and comets were both formed during the earliest days of our Solar System has scientists studying both with keen interest. By examining them up close with satellites and landers — such as the current Rosetta mission with the Philae lander to Comet 67P — scientists hope to learn more about what our Solar System looked like in its earliest days. The next mission to a comet will be the JAXA Hayabusa-2 mission, which should launch at the end of November or early December 2014, arriving in 2018 to asteroid (162173) 1999 JU. Here’s a list of past missions to asteroids and comets.
Scientists also study comets and asteroids to determine the likelihood of them hitting Earth and other planets, and what effect their flybys could have on planetary atmospheres. In November of 2014, a comet named Siding Spring flew very close to Mars, and scientists are still studying the encounter. But this may happen more often that we think: one recent study says that Mars gets bombarded by 200 small asteroids or comets every year.
How likely is it that our planet could be hit by a large asteroid or comet? We do know that Earth has been hit many times in the past by asteroids and comets whose orbits bring them into the inner Solar System. There is strong scientific evidence that cosmic collisions played a major role in the mass extinctions documented in Earth’s fossil records. These objects that come close to Earth, known as Near Earth Objects or NEOs, still pose a danger to Earth today. But NASA, ESA and other space agencies have search programs that have discovered hundreds of thousands of main-belt asteroids, comets. None at this time pose any threat to Earth. You can find out more on this topic at NASA’s Near Earth Object Program website.
Additionally, the possibility of mining both asteroids and comets someday is also becoming a source of interest for industrialists and commercial space ventures, such as Planetary Resources.
Artist's concept of the Dawn spacecraft arriving at Vesta. Image credit: NASA/JPL-Caltech
Vesta is one of the largest asteroids in the Solar System. Comprising 9% of the mass in the Asteroid Belt, it is second in size only to the dwarf-planet Ceres. And now, thanks to data obtained by NASA’s Dawn spacecraft, Vesta’s surface has been mapped out in unprecedented detail.
These high-resolution geological maps reveal the variety of Vesta’s surface features and provide a window into the asteroid’s history.
“The geologic mapping campaign at Vesta took about two-and-a-half years to complete, and the resulting maps enabled us to recognize a geologic timescale of Vesta for comparison to other planets,” said David Williams of Arizona State University.
Geological mapping is a technique used to derive the geologic history of a planetary object from detailed analysis of surface morphology, topography, color and brightness information. The team found that Vesta’s geological history is characterized by a sequence of large impact events, primarily by the Veneneia and Rheasilvia impacts in Vesta’s early history and the Marcia impact in its late history.
The geologic mapping of Vesta was made possible by the Dawn spacecraft’s framing camera, which was provided by the Max Planck Institute for Solar System Research of the German Max Planck Society and the German Aerospace Center. This camera takes panchromatic images and seven bands of color-filtered images, which are used to create topographic models of the surface that aid in the geologic interpretation.
A team of 14 scientists mapped the surface of Vesta using Dawn data. The study was led by three NASA-funded participating scientists: Williams; R. Aileen Yingst of the Planetary Science Institute; and W. Brent Garry of the NASA Goddard Spaceflight Center.
This high-res geological map of Vesta is derived from Dawn spacecraft data. Credit: NASA/JPL-Caltech/ASU
The brown colored sections of the map represent the oldest, most heavily cratered surface. Purple colors in the north and light blue represent terrains modified by the Veneneia and Rheasilvia impacts, respectively. Light purples and dark blue colors below the equator represent the interior of the Rheasilvia and Veneneia basins. Greens and yellows represent relatively young landslides or other downhill movement and crater impact materials, respectively.
The map indicates the prominence of impact events – such as the Veneneia, Rheasilvia and Marcia impacts, respectively – in shaping the asteroid’s surface. It also indicates that the oldest crust on Vesta pre-dates the earliest Veneneia impact. The relative timescale is supplemented by model-based absolute ages from two different approaches that apply crater statistics to date the surface.
“This mapping was crucial for getting a better understanding of Vesta’s geological history, as well as providing context for the compositional information that we received from other instruments on the spacecraft: the visible and infrared (VIR) mapping spectrometer and the gamma-ray and neutron detector (GRaND),” said Carol Raymond, Dawn’s deputy principal investigator at NASA’s Jet Propulsion Laboratory in Pasadena, California.
The objective of NASA’s Dawn mission is to characterize the two most massive objects in the main asteroid belt between Mars and Jupiter – Vesta and the dwarf planet Ceres.
These Hubble Space Telescope images of Vesta and Ceres show two of the most massive asteroids in the asteroid belt. Credit: NASA/European Space Agency
Asteroids like Vesta are remnants of the formation of the solar system, giving scientists a peek at its early history. They can also harbor molecules that are the building blocks of life and reveal clues about the origins of life on Earth. Hence why scientists are eager to learn more about its secrets.
The Dawn spacecraft was launched in September of 2007 and orbited Vesta between July 2011 and September 2012. Using ion propulsion in spiraling trajectories to travel from Earth to Vesta, Dawn will orbit Vesta and then continue on to orbit the dwarf planet Ceres by April 2015.
The high resolution maps were included with a series of 11 scientific papers published this week in a special issue of the journal Icarus. The Dawn spacecraft is currently on its way to Ceres, the largest object in the asteroid belt, and will arrive at Ceres in March 2015.
This diagram maps data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors (bolides). The location of impacts from objects ranging from 1 meter (3 feet) to nearly 20 meters (60 feet) in size such as Chelyabinsk asteroid are shown globally. (Credit: Planetary Science, NASA)
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.
On Feb. 28, 2009, Peter Jenniskens (SETI/NASA), finds his first 2008TC3 meteorite after an 18-mile long journey. “It was an incredible feeling,” Jenniskens said. The meteorite which impacted in the Nubian Desert of Africa on Oct 7, 2008 was the first asteroid whose impact with Earth was predicted while still in space approaching Earth. Meteorite 2008TC3 and Chelyabinsk’s are part of the released data set. (Credit: NASA/SETI/P.Jenniskens)
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.
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 full caption is at bottom. (Credit: P. Brown, Letter to Nature, 2013, Figure 3)
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.
Vivid Vesta Vista in Vibrant 3 D from NASA’s Dawn Asteroid Orbiter. Vesta is the second most massive asteroid and is 330 miles (530 km) in diameter. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
When NASA’s Dawn spacecraft arrived at Vesta in July 2011, two features immediately jumped out at planetary scientists who had been so eagerly anticipating a good look at the giant asteroid. One was a series of long troughs encircling Vesta’s equator, and the other was the enormous crater at its southern pole. Named Rheasilvia, the centrally-peaked basin spans 500 kilometers in width and it was hypothesized that the impact event that created it was also responsible for the deep Grand Canyon-sized grooves gouging Vesta’s middle.
Now, research led by a Brown University professor and a former graduate student reveal how it all probably happened.
“Vesta got hammered,” said Peter Schultz, professor of earth, environmental, and planetary sciences at Brown and the study’s senior author. “The whole interior was reverberating, and what we see on the surface is the manifestation of what happened in the interior.”
Using a 4-meter-long air-powered cannon at NASA’s Ames Vertical Gun Range, Peter Schultz and Brown graduate Angela Stickle – now a researcher at the Johns Hopkins University Applied Physics Laboratory – recreated cosmic impact events with small pellets fired at softball-sized acrylic spheres at the type of velocities you’d find in space.
The impacts were captured on super-high-speed camera. What Stickle and Schultz saw were stress fractures occurring not only at the points of impact on the acrylic spheres but also at the point directly opposite them, and then rapidly propagating toward the midlines of the spheres… their “equators,” if you will.
Scaled up to Vesta size and composition, these levels of forces would have created precisely the types of deep troughs seen today running askew around Vesta’s midsection.
Watch a million-fps video of a test impact below:
So why is Vesta’s trough belt slanted? According to the researchers’ abstract, “experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target.” That is, the impactor that struck Vesta’s south pole likely came in at an angle, which made for uneven propagation of stress fracturing outward across the protoplanet (and smashed its south pole so much that scientists had initially said it was “missing!”)
Close-ups of Vesta’s equatorial troughs obtained by Dawn’s framing camera in August and September 2011. (NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA)
That angle of incidence — estimated to be less than 40 degrees — not only left Vesta with a slanted belt of grooves, but also probably kept it from getting blasted apart altogether.
“Vesta was lucky,” said Schultz. “If this collision had been straight on, there would have been one less large asteroid and only a family of fragments left behind.”
Watch a video tour of Vesta made from data acquired by Dawn in 2011 and 2012 below:
The team’s findings will be published in the February 2015 issue of the journal Icarus and are currently available online here (paywall, sorry). Also you can see many more images of Vesta from the Dawn mission here and find out the latest news from the ongoing mission to Ceres on the Dawn Journal.
