Mountain-size asteroid 2004 BL86 will pass in the vicinity of Earth on January 26, 2015.
The space rock is roughly a third of a mile across.
By comparison, most near-Earth asteroids have diameters no larger than 50 to 100 ft.
But the asteroid is going by at a very safe distance of 745,000 miles. That’s about three times as far away as the Moon.
Asteroid 2004 BL86 is the largest known space rock predicted to come this close to Earth until 2027.Because it’s relatively large, 2004 BL86 will brighten rapidly as it approaches Earth.
Astronomers predict it will become about 9th magnitude for several hours as it passes closest to us. This is still much too faint to be seen by eye, and it is beyond the reach of most binoculars.
However, the asteroid should be bright enough to follow with a 3- or 4-inch-diameter telescope as it moves among the stars.
Observers in the Americas, Europe, and Africa can track down the asteroid during its brightest time: from 8 p.m. EST on Monday evening, January 26, until about 1 a.m. EST on January 27.
During this time 2004 BL86 will be heading northward through the dim constellation Cancer. It skims the eastern edge of a star cluster called the Beehive (or Messier 44) from about midnight to 12:30 a.m. EST.
The asteroid’s closest approach to Earth actually occurs hours earlier, around 11 a.m. EST on the 26th.
However, at that time it’s predicted to be somewhat dimmer, about magnitude 10, because Earth will see only a portion of its illuminated side.
The asteroid brightens, despite the increasing distance, because we’re seeing its face become more fully illuminated.
The space rock will be moving about 2.5° per hour while crossing Cancer. That’s fast enough that you’ll be able to see it moving in real time in a telescopic view whenever it passes close to a background star.
Huge asteroid 1998 QE2, that measures nearly 1.7 miles across, is set to fly past the Earth.
The space rock is so large that it is orbited by its own moon.
It will make its closest approach to our planet at 20:59 GMT, but scientists say there is no chance that it will hit.
Instead it will keep a safe distance – at closest, about 3.6 million miles.
That is about 200 times more distant than the asteroid “near-miss” that occurred in February – but Friday’s passing space rock is more than 50,000 times larger.
Prof. Alan Fitzsimmons, an astronomer at Queen’s University Belfast, said: “It’s a big one. And there are very few of these objects known – there are probably only about 600 or so of this size or larger in near-Earth space.
“And importantly, if something this size did hit us one day in the future, it is extremely likely it would cause global environmental devastation, so it is important to try and understand these objects.”
Huge asteroid 1998 QE2, that measures nearly 1.7 miles across, is set to fly past the Earth
This fly-by will give astronomers the chance to study the rocky mass in detail.
Using radar telescopes, they will record a series of high-resolution images.
They want to find out what it is made of, and exactly where in the Solar System it came from.
Prof. Alan Fitzsimmons said: “We already know from the radar measurements, coupled with its brightness, that it appears to be a relatively dark asteroid – that it’s come from the outer part of the asteroid belt.”
Early analysis has already revealed that the asteroid has its own moon: it is being orbited by another smaller piece of rock that is about 2,000 ft across.
About 15% of asteroids that are large are “binary” systems like this.
This celestial event will not be visible to the naked eye, but space enthusiasts with even a modest telescope might be able to witness the pass.
After this, asteroid 1998 QE2 will hurtle back out into deep space; Friday’s visit will be its closest approach for at least two centuries.
Researchers are becoming increasingly interested in potential hazards in space.
So far they have counted more than 9,000 near-Earth asteroids, and they spot another 800 new space rocks on average each year.
However, other researchers were more cautious about the results.
“The overall aim of our project is to better characterize the impactor that produced the crater in the Yucatan peninsula [in Mexico],” said Dr. Jason Moore, from Dartmouth College in New Hampshire.
The space rock gave rise to a global layer of sediments enriched in the chemical element iridium, in concentrations much higher than naturally occurs; it must have come from outer space.
However, in the first part of their work, the team suggests that frequently quoted iridium values are incorrect. Using a comparison with another extraterrestrial element deposited in the impact – osmium – they were able to deduce that the collision deposited less debris than has previously been supposed.
The recalculated iridium value suggests a smaller body hit the Earth. So for the second part of their work, the researchers took the new figure and attempted to reconcile it with the known physical properties of the Chicxulub impact.
For this smaller space rock to have produced a 180 km-wide crater, it must have been travelling relatively quickly. The team found that a long-period comet fitted the bill much better than other possible candidates.
“You’d need an asteroid of about 5 km diameter to contribute that much iridium and osmium. But an asteroid that size would not make a 200 km-diameter crater,” said Dr. Jason Moore.
“So we said: how do we get something that has enough energy to generate that size of crater, but has much less rocky material? That brings us to comets.”
Researchers have found that the space rock that hit Earth 65 million years ago and was widely implicated in the end of the dinosaurs was likely a speeding comet
Co-author Mukul Sharma, also from Dartmouth College, said: “You would need some special pleading for an asteroid moving very rapidly – although it is possible. But of the comets and asteroids we have looked at in the skies, the comets are the ones that are moving very rapidly.”
Long-period comets are balls of dust, rock and ice that are on highly eccentric trajectories around the Sun. They may take hundreds, thousands or in some cases even millions of years to complete one orbit.
The extinction event 65 million years ago is now widely associated with the space impact at Chicxulub. It killed off about 70% of all species on Earth in just a short period of time, most notably the non-avian dinosaurs.
The enormous collision would have triggered fires, earthquakes and huge tsunamis. The dust and gas thrown up into the atmosphere would have depressed global temperatures for several years.
Dr. Gareth Collins, who researches impact cratering at Imperial College London, described the research by the Virginia team as “nice work” and “thought-provoking”.
He said: “I don’t think it is possible to accurately determine the impactor size from geochemistry.
“Geochemistry tells you – quite accurately – only the mass of meteoritic material that is distributed globally, not the total mass of the impactor. To estimate the latter, one needs to know what fraction of the impactor was distributed globally, as opposed to being ejected to space or landing close to the crater.”
Dr. Gareth Collins added: “The authors suggest that 75% of the impactor mass is distributed globally, and hence arrive at quite a small-sized impactor, but in reality this fraction could be lower than 20%.”
That would easily keep the door open for a bigger, more slowly moving asteroid.
The authors accept this point, but cite recent studies showing suggesting mass loss for the Chicxulub impact was between 11% and 25%.
In recent years, several space objects have taken astronomers by surprise, serving as a reminder that our cosmic neighborhood remains a busy place.
On February 15, 2013, 2012 DA14 – an asteroid as large as an Olympic swimming pool – raced past the Earth at a distance of just 27,700 km (17,200 miles). It had only been discovered the previous year.
And on the same day, a 17 m space rock exploded over Russia’s Ural mountains with an energy of about 440 kilotonnes of TNT. About 1,000 people were injured as the shockwave blew out windows and rocked buildings.
Some 95% of the near-Earth objects larger than 1km have been discovered. However, only about 10% of the 13,000 – 20,000 asteroids above the size of 140m are being tracked.
There are probably many more comets than near-Earth asteroids, but NASA points out they spend almost all of their lifetimes at great distances from the Sun and Earth, so that they contribute only about 10% to the census of larger objects that have struck the Earth.
Asteroid 2012 DA14, a 150-foot space rock orbiting Earth, will pass closer than geostationary satellites to our planet on February next year.
NASA’s Impact Risk report said that the odds of the space rock actually hitting Earth are very low indeed – but on February 15, 2013, it will pass just 17,000 miles from Earth, closer than “geostationary” satellites.
If an asteroid of that size hit Earth, it would cause an explosion similar to a nuclear blast.
Two astronomers from the Observatorio Astronómico de La Sagra in Spain spotted 2012 DA14 in late February and its orbit has been calculated to be very similar to Earth’s.
Some reports suggested that on February 15 next year an impact was a possibility, but U.S astronomer Phil Plait, the creator of the Bad Astronomy blog, has ruled out an impact.
Phil Plait wrote: “Asteroid 2012 DA14 is almost certainly not going to hit Earth next February. And by <<almost certainly>>, I mean it. The odds of an impact are so low they are essentially zero. This does not rule out an impact at some future date, but for now we’re safe.”
Asteroid 2012 DA14, a 150-foot space rock orbiting Earth, will pass closer than geostationary satellites to our planet on February next year
The asteroid will come within 17,000 miles of Earth, which is closer than some of our satellites, but Phil Plait says this is nothing to worry about.
The astronomer adds: “Seventeen thousand miles is well beneath many of our own orbiting satellites. To the best of my knowledge, this is the closest pass of a decent-sized asteroid ever seen before the actual pass itself. However, let’s again be very clear – it will miss. In astronomical terms, 17,000 miles is pretty close, but in real human terms it’s a clean miss.”
After 2013, 2012 DA14’s closest brush with Earth will come in 2020, but Phil Plait said that even then the odds of an impact will be less than the chance of being hit by lightning in your lifetime – 1 in 100,000.
What are the chances of a major impact?
NASA’s latest scan for “impact event” threats used the Wide-field Infrared Survey Explorer, or WISE and took two infrared scans of the entire celestial sky between January 2010 and February 2011.
The scan aimed to find asteroids and comets “near Earth” – i.e. within 120 million miles.
The scan found there are 20,500 asteroids and comets that could destroy a city-sized area within 120 million miles of earth – previously the figure was thought to be 36,000.
NASA says the risk of impact is less than previously thought. The likelihood of a “planet-killer” – the mountain-sized asteroids in the “large-sized” range, above 3,300ft – appears to have fallen more significantly.
There are only 981 of these objects near Earth, and NASA has found 911 of them.