Asteroid Apophis: Dealing with Earth’s Future Troublemaker

by Leonard David, Senior Space Writer Date: 03 November 2005 Time: 09:58 AM ET

The most likely path of asteroid 2004 MN4 on April 13, 2029 will bring it so close to Earth that gravity will significantly alter its course. CREDIT: NASA/JPL

BOULDER, Colorado – The potential for a newly discovered asteroid smacking into the Earth in 2036 cannot be discounted. NASA has sketched out a response strategy in the outside possibility that the space rock becomes a true threat.

NASA’s action plan was the result of prodding by a group of astronauts, scientists and other technical specialists uneasy about the current lack of action to protect the Earth from the impact of near Earth objects (NEOs).

The object was found last year through the efforts of NASA’s Spaceguard Survey. In 1998 NASA formally initiated the Spaceguard Survey by adopting the objective of finding 90 percent of the near Earth asteroids larger than 3,280 feet (one kilometer) diameter within the next decade – before the end of 2008.

Asteroid 99942 Apophis – first labeled as 2004 MN4 — is estimated to be roughly 1,000 feet (320 meters) in diameter. Were it to strike Earth, it would not set off global havoc but would generate significant local or regional damage, experts say.

Worrisome to asteroid watchers is the exceptionally close flyby of Earth by Apophis on April 13, 2029. So close in fact, the space rock will be naked-eye visible as it darts by. And what can’t be ruled out at this time is that Apophis may pass through a gravitational “keyhole” – a spot that alters the asteroid’s trajectory as it zips by our planet and might put it on the bee-line lane for banging into Earth seven years later.

Issue of critical importance

Concern over asteroid Apophis and the ability to precisely chart its trajectory — and take steps if needed to deflect the object — were fervently voiced by the B612 Foundation, chaired by Russell Schweickart, a former Apollo astronaut.

The group requested that NASA carry out an analysis that included the possibility of placing an active radio transponder on the object. Doing so at a fairly early date would yield the requisite orbital accuracy of the asteroid as it sped through space.

In a June 6 letter to NASA Administrator, Michael Griffin, Schweickart on behalf of the B612 Foundation called for support in “resolving an issue of critical importance” – namely whether a scientific mission should be launched to asteroid Apophis in the near term.

Such a probe, if dispatched, Schweickart stated, would provide knowledge of the asteroid’s orbit in time to initiate a deflection mission in the unlikely event one should be required. The position of the B612 Foundation was that the mission should be staged, pointing out that NASA’s NEO program personnel apparently did not concur with that view. A spacecraft mission to Apophis would augment tracking of the object from the ground, the letter to Griffin explained, and also carry out a number of scientific duties too.

NASA response

NASA provided a formal response to the B612 Foundation’s June communique via an October 12 letter from Mary Cleave, Associate Administrator for Science Mission Directorate.

That NASA reply came with an appended detailed analysis by Steven Chesley of NASA’S NEO Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The study by Chesley dug into Apophis’ orbit, under varying conditions, and contained other items pertaining to the space agency’s findings about the Apophis matter.

“The key conclusion to be taken from this analysis,” Cleave explained in the letter, “is that aggressive (i.e., more expensive) action can reasonably be delayed until after the 2013 observing opportunity. For Apophis, the 16 years available after 2013 are sufficient to recognize and respond to any hazard that still exists after that time.”

Cleave noted in the letter that while Apophis “is an object whose motion we will continue to monitor closely in the coming years, we conclude a space mission to this object based solely on any perceived collision hazard is not warranted at this time.”

Not ruled out by Cleave, however, is the prospect of Discovery-class, low-cost missions sent to Apophis, “based on purely scientific arguments,” she said.

“Indeed, the asteroid’s orbit is particularly attractive for spacecraft rendezvous, and the extraordinary close encounter in April 2029 provides a unique opportunity to investigate a number of scientific NEO issues,” Cleave explained in the letter.

Pinpointing the object’s whereabouts

While Schweickart said that the NASA response to the B612 Foundation’s concern is a step forward, there are other issues still to be resolved.

One matter involves radar tracking of Apophis.

On one hand, radar plays a crucial role in being able to rationally determine the future likelihood of a NEO impact and potentially in planning for a deflection mission when required.

Yet the availability of NEO radar tracking, and the budgets to support this work in the future is highly uncertain, even precarious, Schweickart and the B612 Foundation emphasize. Radar hits of Apophis at each opportunity through 2021 are important to keep watch of the object’s whereabouts.

“Tracking these asteroids once you know they exist and pinning down their orbits is really not science,” Schweickart told “This is public safety. It’s disaster preparedness.”

Begging time and bumming bucks

When Apophis swings by Earth, Schweickart said the asteroid will likely change its orbit. Also, its spin characteristics may be altered. Due to Earth’s gravity tugging on the object, “asteroid quakes” could reshape Apophis, he said.

Moreover, still far from resolution is a “who’s in charge” proclamation about troublemaking NEOs, Schweickart said.

“It would be great if we had NASA doing this as a regular process. Unfortunately, the mindset that’s essentially required by their budget is to think about discovery, not to think about the potential need for deflection,” Schweickart added. “Until your mindset is oriented that way, you’re going to miss things.”

Until an agency is identified that is responsible for all of this, Schweickart cautioned, everybody is “begging time and bumming bucks” from some other program. “This whole thing is sort of in a precarious position until somebody gets around to assigning agency responsibility,” he said.

Japan’s Hayabusa mission

Regarding the skill required to deposit a transponder on Apophis, Schweickart saluted Japan’s Hayabusa asteroid sample-return mission, now in progress.

That craft is scheduled to make two landings on its target asteroid – Itokawa — later this month. The mission is geared to haul back samples of the object to Earth.

Scientists at Japan’s Institute of Space and Astronautical Science (ISAS) are working day-by-day issues in readying the probe for contact with the asteroid, including release of a mini-robot onto Itokawa that will move about and survey its rocky surroundings. ISAS is a research arm of the Japan Aerospace Exploration Agency (JAXA).

“It’s an impressive mission,” Schweickart said, sure to yield operational experience and lessons learned on how best to execute duties on asteroid Apophis.

Global preparedness

The ruin stemming from asteroid Apophis colliding with Earth would potentially be very great.

Indeed, the consequences, Schweickart suggested, would dwarf those seen as a result of the Indian Ocean tsunami in December 2004, hurricanes Katrina and Rita in September of this year, and the Pakistan earthquake last month.

In regards to global preparedness in handling these unusually devastating events of late, “it’s basically out of sight…out of mind,” Schweickart said. “That’s the real challenge for society. The things that you don’t know about are one thing. But the things that you do know about, and don’t do something about…those are the ones that are really tough.”

Refine the impact probability

Fully concurring with NASA’s response is Alan Harris, a senior research scientist and asteroid expert for the Space Science Institute headquartered here.

Harris noted, as has been underscored by the B612 Foundation, that if Apophis is indeed on an impact trajectory, then ground-based radar observations will not be able to refine the impact probability to greater than 20 percent. “That is, we would still not know better than one-chance-in-five whether the impact would really occur or not,” he told

“We really would need a transponder to improve tracking enough to firmly establish that an impact would occur,” Harris said.

What has been overlooked, or at best under-emphasized, Harris added, is a point raised in the NASA response. Ground-only tracking has a 99.8 percent chance of eliminating any chance at all of an impact. Thus, there is only one-chance-in-500 that ground-based tracking will fail to resolve the issue in favor of no impact. “For this reason I think the NASA conclusion is entirely sensible,” he said.

Wait and see strategy

Harris said that there are Apophis observing opportunities every 6-8 years, with each one having about a 90 percent chance of eliminating any possible impact. At each of these “shoulder” times, he said, one can re-evaluate the “wait and see” strategy if the impact possibility does not go away.

“Certainly it seems appropriate to play the ‘wait and see’ game until after the 2013 observing opportunity,” Harris stated. None of this diminishes the opening that Apophis presents for purely scientific investigations, which could incidentally contribute to the NEO hazard issue, he said.

Harris said that he would not recommend a “deep impact” type of scientific mission, “lest we have the misfortune to deflect it into a keyhole, but other than that, Apophis is a very attractive mission target.”

A coming of age

Asteroid Apophis, and the discussions it has sparked are welcomed, observed David Morrison, a space scientist and asteroid specialist at NASA’s Ames Research Center, situated in Silicon Valley, California.

“I am pleased that this dialog is taking place,” Morrison said. “This is the first time that serious possibilities for dealing with a real but low-probability future impact have been discussed in a technically professional way, rather than receiving the ‘Hollywood treatment'”.

Morrison said that he considers it remarkable that the Spaceguard Survey has reached the
level of maturity where such an asteroid could not only be found, but its orbit understood well enough to deal with “keyholes” and other subtleties. “Apophis represents for me a symbol of the coming of age of Spaceguard and of asteroid impact studies in general,” he said.

The possibility of Apophis hitting Earth on April 13, 2036 is real, Morrison said, even if the probabilities now seem to be very small. “These probabilities represent uncertainties in our knowledge of the orbit, not a failure of the science.”

But whether the asteroid will strike Earth or not, Morrison concluded, the challenge is to resolve which case is correct. “With more observations over a longer time span, we will be able to tie this down.”

via Asteroid Apophis: Dealing with Earth’s Future Troublemaker |


Astronomers Gear Up for Historic Asteroid Pass in 2029

by Ker Than, Staff Writer Date: 22 August 2005 Time: 06:30 AM ET

During the early morning hours of April 13, 2029, observers in Asia and North Africa will have a chance to witness a rare celestial event as an asteroid, 99942 Apophis, passes within 20,000 miles of Earth.

"It’s not gonna knock your socks off, and it certainly won’t be the brightest object in the sky, but it’ll be easily observable with the naked eye," said Don Yeomans, manager of NASA’s Near Earth Object (NEO) Program.

The approach of an asteroid this large — Apophis is more than 1,000 feet in diameter — and this close to Earth occurs only about once every 1,500 years.

Scientists are awaiting the close flyby with mixed emotions: excitement at a unique scientific opportunity and uneasiness that it might be a sign of more ominous things to come.

Inside look

A team of researchers headed by Daniel Scheeres, an aerospace engineer from the University of Michigan, hopes to take advantage of Apophis’ close approach to learn more about how asteroids are assembled and to gather information about seismic activity inside the rock.

The beauty of this event is that it is a kind of natural experiment that scientists would never be able to recreate, Scheeres told in an email interview.

Tidal forces from Earth’s gravity will twist and churn the asteroid’s insides and deform its exterior as it passes by the planet. Scheeres said that currently, the plan is to use ground-based radar to monitor the asteroids movements and telescopes to observe changes in its surface features and rotation.

But even the most sophisticated ground-based observations won’t be sufficient for gathering detailed information about the interior of the asteroid, Scheeres said.

That kind of detail would require that a network of probes capable of measuring acceleration and seismic activity be embedded in the asteroid’s surface. Another possibility would be to place a probe in orbit around the asteroid in order to keep tabs on it and to map its surface. No such space missions are currently in the works, however.

Apophis was discovered last year and is named after a snakelike Egyptian god of darkness and chaos. The name is appropriate. For a brief period of time last winter, scientists had given Apophis, then known as 2004 MN4, a 1-in-40 chance of colliding with Earth in 2029.

Additional observations ruled out the 2029 impact, and scientists now predict there is about a 1-in-10,000 chance that the asteroid will hit Earth in 2036, on yet another of its trips around the Sun on a course that crosses the orbit of Earth.

A large part of the uncertainty surrounding Apophis’ movements is due something called the Yarkovsky Effect. When rotating bodies like asteroids pass through our solar system, they absorb solar radiation from the Sun that they then re-radiate.

The miniscule but persistent pressure from this re-radiation can cause a rock to speed up or slow down and change its flight path.

In many ways, the hubbub surrounding Apophis stems from an unusual confluence of events as the detection of near-Earth objects coincides roughly with humanity’s demonstrated ability to meet them. Emboldened by the success of recent missions like Stardust and Deep Impact, some scientists think it prudent to launch a space mission to determine whether Apophis poses a significant threat.

Let’s go!

Astronomers know that in 2029, Apophis’ path will be bent significantly by Earth’s gravity. They don’t know the exact outcome.

In May, former Apollo astronaut Rusty Schweickart sent a letter to NASA administrator Mike Griffin urging the agency to investigate whether in 2029 Apophis might enter certain gravitational “keyholes” near Earth that would alter the asteroid’s flight path in a manner that could put it on a more certain collision course with our planet in 2036.

In order to more accurately track its movements, Schweickart also proposed launching a space mission to place a radio transponder on Apophis. An official to response to Schweickart’s letter is expected from NASA within the next few weeks.

As demonstrated by the Deep Impact mission, in which NASA smacked a comet with a small probe, it is possible to strike a fast moving body in space using current technologies.

“You don’t have to change the course of the comet very much to miss the keyhole if you do it a number of years in advance,” said Clark Chapman, an astronomer at the Southwest Research Institute in Colorado who has served on a number of committees concerning near-Earth objects.

Chapman urges caution, however, and said that scientists shouldn’t rush to action. “You don’t want to nudge it until you know what the nudge is going to do,” Chapman said. The worst thing that could happen, of course, would be to nudge the asteroid in the wrong direction, based on the incomplete data now in hand, and actually cause a future collision.

Sooner rather than later

Most scientists agree that 2029 is the absolute deadline if an intervention mission is to be launched. After 2029, the distance Apophis would need to be moved in order to avoid an impact would be too great given current technologies.

In his letter, Schweickart said plans for a space mission to place a transponder on the Apophis should be in place by 2014 and that an intervention mission, should it prove necessary, be launched prior to 2029.

However, Apophis will veer within an observable distance of Earth twice more before 2029 — once in 2013 and again in 2021. Based on data collected from those two flybys, Yeomans said scientists should be able to conclude with 99.8 percent accuracy whether a future impact scenario can be ruled out and he believes we should therefore wait before launching a mission that could cost hundreds of millions of dollars.

Until then, Yeomans says he won’t be losing sleep over Apophis.

“It’s an interesting object and it’s raised some interesting issues, but a worrisome threat? No,” said Yeomans. “We’ve got plenty of time.”

via Astronomers Gear Up for Historic Asteroid Pass in 2029 |

Friday the 13th, 2029

Friday the 13th, 2029

Asteroid 2004 MN4 will come scarily close to Earth on April 13, 2029, but it will not hit.

May 13, 2005: Friday the 13th is supposed to be an unlucky day, the sort of day you trip on your shoe laces or lose your wallet or get bad news.

But maybe it’s not so bad. Consider this: On April 13th–Friday the 13th–2029, millions of people are going to go outside, look up and marvel at their good luck. A point of light will be gliding across the sky, faster than many satellites, brighter than most stars.

What’s so lucky about that? It’s asteroid 2004 MN4 … not hitting Earth.

For a while astronomers thought it might. On Christmas Eve 2004, Paul Chodas, Steve Chesley and Don Yeomans at NASA’s Near Earth Object Program office calculated a 1-in-60 chance that 2004 MN4 would collide with Earth. Impact date: April 13, 2029.

The orbits of Earth and asteroid 2004 MN4.

The asteroid is about 320 meters wide. “That’s big enough to punch through Earth’s atmosphere,” devastating a region the size of, say, Texas, if it hit land, or causing widespread tsunamis if it hit ocean, says Chodas. So much for holiday cheer.
Asteroid 2004 MN4 had been discovered in June 2004, lost, then discovered again six months later. With such sparse tracking data it was difficult to say, precisely, where the asteroid would go. A collision with Earth was theoretically possible. “We weren’t too worried,” Chodas says, “but the odds were disturbing.”

This is typical, by the way, of newly-discovered asteroids. Step 1: An asteroid is discovered. Step 2: Uncertain orbits are calculated from spotty tracking data. Step 3: Possible Earth impacts are noted. Step 4: Astronomers watch the asteroid for a while, then realize that it’s going to miss our planet.

Killer Asteroid! headlines generally appear between steps 3 and 4, but that’s another story.

Astronomers knew 2004 MN4 would miss Earth when they found pictures of the asteroid taken, unwittingly, in March 2004, three months before its official discovery. The extra data ruled out a collision in 2029.

Instead, what we’re going to have is an eye-popping close encounter:

On April 13, 2029, asteroid 2004 MN4 will fly past Earth only 18,600 miles (30,000 km) above the ground. For comparison, geosynchronous satellites orbit at 22,300 miles (36,000 km). “At closest approach, the asteroid will shine like a 3rd magnitude star, visible to the unaided eye from Africa, Europe and Asia–even through city lights,” says Jon Giorgini of JPL. This is rare. “Close approaches by objects as large as 2004 MN4 are currently thought to occur at 1000-year intervals, on average.”

Track the orbit of 99942 Apophis (2004 MN4) at NASA’s JPL Small-Body Database.

The asteroid’s trajectory will bend approximately 28 degrees during the encounter, “a result of Earth’s gravitational pull,” explains Giorgini. What happens next is uncertain. Some newspapers have stated that the asteroid might swing around and hit Earth after all in 2035 or so, but Giorgini discounts that: “Our ability to ‘see’ where 2004 MN4 will go (by extrapolating its orbit) is so blurred out by the 2029 Earth encounter, it can’t even be said for certain what side of the sun 2004 MN4 will be on in 2035. Talk of Earth encounters in 2035 is premature.”

In January 2004, a team of astronomers led by Lance Benner of JPL pinged 2004 MN4 using the giant Arecibo radar in Puerto Rico. (Coincidentally, the Arecibo dish is about the same size as the asteroid.) Echoes revealed the asteroid’s precise distance and velocity, “allowing us to calculate the details of the 2029 flyby,” says Giorgini, who was a member of the team along with Benner, Mike Nolan (NAIC) and Steve Ostro (JPL).

More data are needed to forecast 2004 MN4’s motion beyond 2029. “The next good opportunities are in 2013 and 2021,” Giorgini says. The asteroid will be about 9 million miles (14 million km) from Earth, invisible to the naked eye, but close enough for radar studies. “If we get radar ranging in 2013, we should be able to predict the location of 2004 MN4 out to at least 2070.”

The Arecibo radar in Puerto Rico is coincidentally about the size of asteroid 2004 MN4.

The closest encounter of all, Friday the 13th, 2029, will be a spectacular opportunity to explore this asteroid via radar. During this encounter, says Giorgini, “radar could detect the distortion of 2004 MN4’s shape and spin as it passes through Earth’s gravity field. How the asteroid changes (or not) would provide information about its internal structure and material composition.” Beautifully-detailed surface maps are possible, too.

The view through an optical telescope won’t be so impressive. The asteroid’s maximum angular diameter is only 2 to 4 arcseconds, which means it will be a starlike point of light in all but the very largest telescopes.

But to the naked eye–wow! No one in recorded history has ever seen an asteroid in space so bright.

Friday the 13th might not be so bad after all.

via Friday the 13th, 2029 – NASA Science.