Radar image of 1950 DA acquired by the Arecibo Observatory on March 4, 2001 (NASA/JPL/S. Ostro)
Asteroids and comets capture the human imagination unlike any other objects in space. They're speedy, craggy, not too far away -- and dangerous. Geologic investigations around the globe guarantee a sizeable space rock is bound to kiss our fragile blue marble within the next few centuries years. And if one may have wiped out the dinosaurs, the thinking goes, why not us? Browse through 10 of our favorite ominous objects that astronomers have plucked from the foreboding skies.
Asteroid 951, also known as Gaspra, is safely tucked away within the Asteroid Belt between Mars and Jupiter. For now. This image is the outcome of the very first robotic rendezvous with an asteroid. The Galileo spacecraft swung by Gaspra at about 1,000 miles away in November 1991 on its way to Jupiter. The intel Galileo brought back on the asteroid was breathtaking; Gaspra's irregular, tooth-like shape and lack of big craters suggest that it was born out of a recent (300 to 500 million-year-old) smashup in the Asteroid Belt.
What asteroid was the first known to have a mini-companion orbiting it? Asteroid 243, better known as Ida. The Galileo spacecraft also scouted out this 1,900-by-2,375 mile space rock during the long trip to Jupiter in August 1993. Ida spins around once about every 4 1/2 hours, and its little "moon" Dactyl is roughly 20 times smaller. Like asteroid Gaspra, Ida is oddly shaped -- yet unlike Gaspra, Ida has remained in one piece for much of the solar system's 4.5 billion year existence.
NASA's Galileo spacecraft was first to get up close and personal with an asteroid, but the Near-Earth Asteroid Rendezvous (NEAR) mission quickly stole all of the thunder. Designed specifically to study asteroids close to Earth, NEAR's main objective was to spy on 433 Eros. Second only to 1036 Ganymed, Eros is one of the largest asteroids drifting dangerously close to Earth. Measuring 21 by 7 by 7 miles, its size easily rivals the space rock thought to have wiped out the dinosaurs. This false-color image shows where the asteroid's surface is denser (red) and less dense (blue) compared to an average reading.
Itokawa (asteroid 25143) may look like a harmless, peanut-shaped pile of rubble -- but the writing is on the wall. In a few million years, it's probably going to wallop Earth. Hayabusa, Japan's asteroid-snooping spacecraft, was set to land on a smooth patch, scoop up a sample and return it to Earth. Although the plucky robot never did make contact, its payload -- set to arrive at Earth by June 2010 -- probably contains at least a few bits of dust and other material from Itokawa. If it returns safely, Hayabusa will be only the second spacecraft to bring back a sample of the solar system from beyond the moon.
No robot has come out to meet New Jersey-sized asteroid 216 Kleopatra. Rather, this series of images was put together by the expansive Arecibo Observatory in Puerto Rico in mid-2000. As for Kleopatra's dog bone shape? Likely the leftovers of a violent collision within the Asteroid Belt that stuck two similarly sized space rocks together.
Northwestern Univ./Johns Hopkins Univ.
When it comes to 253 Mathilde, it's a wonder there's any asteroid left at all. This pockmarked, porous wad of rock is denser on its surface than it is at its core -- a complete puzzle to scientists. The leading explanation? Constant pounding from impacts squashed Mathilde's surface into a compact layer of rock. Clockwise, from top left: Mathilde in true color; Mathilde's color enhanced; Mathilde in black and white, as seen by the NEAR spacecraft.
Tempel 1 is a comet, not an asteroid, but in fact the difference between the two types of wayward objects is still poorly understood. What appear to be plain ol' asteroids sometimes erupt into comets as they swing by the sun and heat up, sporting beautiful ionic tails. To better understand the difference, NASA smashed a robot called Deep Impact (scientific pun intended) into this wily comet. The probe created some July 4th fireworks in 2005 by deliberately slamming into the 3.1-by-4.3 mile core, directly between the two dark-rimmed craters at far right. Talk about a hole-in-one.
NASA/Lance Benner, JPL
In a few centuries, this ominous-looking asteroid known as 1999 JM8 may impact the Earth, putting it on the "watch out!" list for humans. Astronomers used deep-space radar to create these snapshots of the asteroid in 1999 as it tumbled through space. Clockwise, from top left: July 28; Aug. 1; Aug. 2; Aug. 5.
Also known as comet 81P, Wild 2 used to have a near-perfect circular orbit for billions of years -- that is, however, until Jupiter pulled it into a more eccentric loop around the sun. NASA's Stardust spacecraft sampled bits of the comet's tail and was the first-ever mission to return a sample of material from beyond the moon safely to Earth. Shown here is the comet's 3.1-mile-wide nucleus as seen by Stardust on Jan. 2, 2004.
Courtesy of Celestia Motherlode
Asteroid Apophis is last on our list, and certainly not the best. It is, after all, named after the Egyptian god of "uncreation" for a reason. Known in scientific circles as both 2004 MN4 and 99942 Apophis, this 885-foot-long space rock used to have a fairly good chance of impacting the Earth within a quarter century. After making a breathtakingly close pass on Friday the 13th in April 2029 -- less than 10 percent of the distance between Earth and the moon -- Apophis was thought to have a 1 in 45,000 chance of hitting Earth in 2036 when it swings back around. However, recent calculations have reduced this risk to a 1 in 250,000 chance. Phew! Despite Apophis' diminished threat to Earth, some scientists advocate sending a transmitter to the asteroid's surface to better track its movement. And now, Russia wants to send a deflection mission there, 'just in case' the calculations wrong.
Slide show presentation originally compiled by Dave Mosher.
There are over 10,000 near-Earth objects (NEOs) that have been identified so far — asteroids and comets of varying sizes that approach the Earth’s orbital distance to within about 28 million miles (45 million km). Of the 10,000 discoveries, roughly 10 percent are larger than six-tenths of a mile (one kilometer) in size — large enough to have disastrous global consequences should one impact the Earth.
This is one of them.
First discovered in February 1950, 1950 DA is a 1.1-kilometer-wide asteroid that was observed for 17 days and then disappeared from view. Then it was spotted again on Dec. 31, 2000 — literally on the eve of the 21st century. Coupled with radar observations made a few weeks later in March 2001 it was found that, along with a rather high rotation rate (2.1 hours), asteroid 1950 DA has a trajectory that will bring it very close to Earth on March 16, 2880. How close? Close enough that, within a specific 20-minute window, a collision can not be entirely ruled out.
The image above was made from radar observations by the Arecibo Observatory in Puerto Rico in March 2001, when 1950 DA passed within 7.8 million kilometers (4.8 million miles) of Earth. Is this the mug shot of a future continent-killer?
Radar analysis and research of 1950 DA performed by NASA’s Jet Propulsion Laboratory scientists J.D. Giorgini, S. J. Ostro, Don Yeomans and several others from JPL and other institutions revealed that the impact probability from 1950 DA in March 2880 is, at most, 1 in 300 based on what is known about the asteroid so far.
1 in 300 may sound like a slim chance, but actually this represents a risk 50% greater than that of the average hazard due to all other asteroids from now to then.
However, that’s a maximum value. The study also noted the collision probability for 1950 DA as being in the range from 0 to 0.33%. That upper limit could increase or decrease as more is learned about the asteroid. (The next opportunity for studying 1950 DA via radar is in 2032.)
There are many factors that influence the path of an asteroid through space. Its spin rate, reflectivity (albedo), composition, mass, terrain variations… gravitational interactions with other bodies, some of which may not even have been discovered yet… all of these can affect the movement of an asteroid and, more specifically, its exact position at a future point in time. While many of these things still aren’t precisely known for 1950 DA, one in particular could end up being the saving grace for our descendants: the Yarkovsky effect.
A small but important force acting upon asteroids, the Yarkovsky effect is a “nudge” created by thermal emission. As an asteroid gathers heat energy from the sun, it releases some of that energy back into space. Thanks to Newtonian mechanics the sheer act of doing so creates a physical push back on the asteroid itself, altering its course ever so slightly. Over a long span of time, this slight alteration could result in the relocation of 1950 DA away from the spot in space where Earth will be on March 16, 2880… at least enough so that a miss is certain.
Frame from an animation of 1950 DA rotating.
In fact, recent research by JPL scientists D. Farnocchia and S.R. Chesley have taken into consideration the Yarkovsky effect on 1950 DA based on known values from previous observations, as well as new research suggesting that the asteroid has a retrograde rotation. While their latest assessment does put the risk of an impact in 2880 within the lower end of the probability spectrum (4×10^-4, or -0.58 on the Palermo Scale) it is still far from zero, and in fact remains higher than any other known potential impacts.
So what would happen if the half-mile-wide 1950 DA were to hit Earth? While that depends on a lot of things, such as its composition, speed, angle of impact, where it impacts, etc., needless to say it would cause a lot of damage across a large area. I’m talking an energy release upwards of half a million megatons, which, were it to strike say, New York City, everything within at least a 100-mile radius would be flattened by the force of the impact alone — that’s halfway to Boston and Washington, DC (source). And that’s not even taking into consideration the air blast, atmospheric dust cloud, secondary impacts from debris, or damage from any resulting tsunami (if the impact were in the ocean)… the destruction would easily extend out many more hundreds of miles, and the repercussions — physical, financial, economic, and emotional — would extend around the globe.
Put it this way: if a 40-meter object could do this, imagine what a 1-kilometer one would do.
But again, precisely where 1950 DA will be in another 866 1/2 years (and whether or not it will occupy the same point in space as our planet) relies on many factors that aren’t well known — even though its orbit is pretty well understood. More in-depth observations will need to be made, and that is why asteroids like this must be carefully — and continually — watched.
Luckily, 35 generations offers plenty of time to improve our knowledge. According to JPL’s Near-Earth Object program, “If it is eventually decided 1950 DA needs to be diverted, the hundreds of years of warning could allow a method as simple as dusting the surface of the asteroid with chalk or charcoal, or perhaps white glass beads, or sending a solar sail spacecraft that ends by collapsing its reflective sail around the asteroid. These things would change the asteroids reflectivity and allow sunlight to do the work of pushing the asteroid out of the way.”
Still, whether because of ongoing research, faith in future generations of scientists, or just sheer probability, JPL remains confident that 1950 DA should cause little concern. “The most likely result will be that St. Patrick’s Day parades in 2880 will be a little more festive than usual as 1950 DA recedes into the distance, having passed Earth by.”
Let’s just hope the luck of the Irish is with our planet big time that year…
Learn more about ongoing NEO research on the JPL site here, and find out about asteroid-hunting programs like NASA’s repurposed WISE spacecraft and the proposed Sentinel spacecraft from the B612 Foundation. Because in order to learn more about NEOs, we first need to find them (and there are a lot more out there where 1950 DA came from!)