The asteroid Apophis, forecast to miss Earth by cosmic inches in 2036, may still pose a threat in the foreseeable future.
On Wednesday, radar observations made by NASA using the 230-foot (70-meter) Goldstone radio dish in California determined that the 885 foot wide space rock will probably pass Earth at a distance somewhere between 14 million (0.15 AU) and 36 million miles (0.39 AU).
“We have effectively ruled out the possibility of an Earth impact by Apophis in 2036,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory (JPL). “The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036. Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future.”
Astronomers still lack the data necessary to determine how the asteroid is spinning or how solar radiation might affect its orbital path — a phenomenon called the Yarkovsky effect. According to Jon Giorgini, who developed JPL’s online database Horizons to track objects in the solar system, the effect still won’t put Apophis on a collision path in 2036 even under the worst-case scenario. But the asteroid could pose a very real threat in the decades or centuries ahead.
“There’s a non-linear amplification that can really move it around more,” said Giorgini.
When Apophis was discovered in 2004, astronomers gave it a 1-in-40 chance of colliding with our planet in 2029, making headlines across the globe. Further data eliminated the risks for 2029, revealing that the rock could nonetheless pass within 20,000 miles of our planet– enough for Earth’s gravity to pull Apophis onto a collision course in 2036. Luckily, the latest observations show that the asteroid will miss this half-mile-wide ‘keyhole’ by a wide margin.
The asteroid, also called 2004 MN4, is sufficiently big that it could take out an entire city if it struck land, or slam into the ocean with enough force to generate destructive tsunami waves. While it seems we now don’t have to worry about such a catastrophic event within the next 20 years or so, the uncertainty surrounding the issue is itself a cause for concern.
A few weeks ago scientists using the huge Gemini telescope in Hawaii proved that a similarly threatening asteroid called 2011 AG5 would miss its 217-mile-wide keyhole in 2023, lessing the prior 1 in 500 odds of a collision in 2040.
“A point to be realized is that while the chances of impact in these cases are very low by ordinary standards, they aren’t zero,” said Clark Chapman, senior scientist at the Southwest Research Institute. “The consequences of an impact could be very terrible, so it is important to plan and prepare for the possibility of impact until it is ruled out.”
Just how do we plan and prepare for an asteroid collision with Earth? “This is the biggest problem for planetary defense,” said Andrew Cheng, a physicist at the Applied Physics Laboratory at Johns Hopkins. “There is a risk if we saw an asteroid coming towards us, we wouldn’t know if we could do anything about it.”
Last month Cheng proposed a test mission to deflect a small asteroid called Didymos due to pass Earth in 2022. The mission would involve NASA ramming the rock with a 600-pound spaceship, while the European Space Agency monitored the collision with their Asteroid Impact and Deflection Assessment (AIDA) spacecraft.
This would be an important first step in gauging and developing our ability to avert potential ‘doomsday’ asteroids in the future. Chapman mentioned the importance of building humankind’s capability to deflect asteroids with regard to the timing of recent studies on asteroid AG5.
“It was important to get these observations of AG5 in the autumn of 2012,” Chapman said, “because if it had turned out that AG5 was actually on an impact trajectory, it would have given us an additional year to mount a deflection mission and succeed in deflecting it from the 2023 keyhole.”
Continued radar observations from the Goldstone dish in California and the Arecibo Observatory in Puerto Rico should give astronomers a much better understanding of Apophis’ spin, size, and trajectory. After these factors are accounted for, the Jet Propulsion Observatory will update its official risk assessment for Apophis. Whether or not we can take it off the hit list permanently, many contend that we must be ready to face other threats.
“I’m hoping that we don’t follow the bad precedent of stating that the risk from Apophis has been eliminated,” said Apollo 9 astronaut Rusty Schweickart, a leader in raising awareness about the threats and opportunities presented by near-Earth objects, in an interview with NBC News. “Please look on the JPL risk page and especially the more detailed info and note that 1) The 2036 impact possibility is, while significantly reduced, still possible, and 2) that the 2068 impact possibility is now elevated … to a level that exceeds what the 2036 impact was prior to this apparition.”
“Until JPL and the other guys get more data, enough to really define the Yarkovsky effect,” Schweickart continued, “we really won’t be able to get definitive data for longer time scales that we can rely on.”
The good news is that our species now has the observational technology to spot asteroids that pose a risk to the Earth several decades in advance. The bad news is that we are still completely unprepared to deflect a large rock if it is in fact on a collision course with our planet.