This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

15 June 2012

NASA Releases Workshop Data And Findings On Asteroid 2011 AG5

A recent NASA workshop has indicated that Asteroid 2011 AG5, a 140 m wide asteroid discovered in early 2011, has a very small chance (0.2%) that it could impact the Earth in February 2040. Attendees expressed confidence that in the next four years, analysis of space and ground-based observations will show the likelihood of 2011 AG5 missing Earth to be greater than 99 percent.

There is a NASA news release on this workshop. Here are several PDF documents from the workshop at NASA Goddard: Asteroid 2011 AG5 Documents (May-June 2012)

JPL Report on 2011 AG5
The Executive Summary of the JPL Report on 2011 AG5
The Consensus Summary for the Goddard Workshop held on May 29, 2012

Orbit and current location (6/15/2012) of asteroid 2011 AG5. Image credit: NASA/JPL-Caltech

 (Source: Lindley Johnson, NASA HQ NEO Office)
 (Source: JPL Report on 2011 AG5)
Fig. 8. A “keyhole map” for 2011 AG5 in the 2023 b-plane (Source: JPL Report on 2011 AG5)

Summary of Findings from the workshop:

Summary of Potentially Hazardous Asteroid Workshop Findings
Held 29 May, 2012, at Goddard Space Flight Center

• Near Earth Object 2011 AG5 is a Potentially Hazard Asteroid (PHA) discovered by the NASA supported Catalina Sky Survey on January 8, 2011. Due to the limited observations collected on this object to date, within the current uncertainty of the asteroid’s predicted orbit positions is a 0.2% chance that asteroid 2011 AG5 could impact the Earth in February 2040. Should such an impact occur, the estimated 140 meter-sized asteroid could create an energy release roughly equal to 100 megatons TNT.

• The 2040 impact would occur only if the asteroid first passes through a 365 kilometer region in space, called a “keyhole”, as it passes within a few million kilometers of Earth during February 2023. There is likewise only a 0.2% chance of this occurring, given our current understanding of its orbit.

• The asteroid is currently unobservable as it is in the daytime sky, but when it becomes easily observable again in Fall 2013, the data expected to be collected will improve our computation of its orbit and could drop the position uncertainty at the 2040 Earth-encounter from its current area of over 200 Earth diameters down to 2-3 Earth diameters. Additional observations expected in 2015-2020 could reduce this uncertainty further.
- Observations of the asteroid earlier than Fall 2013 would be useful, but the object is small, distant and spends much of the time until then on the opposite side of the Sun. Only the largest ground and space telescopes have even a fleeting opportunity to observe it.

• Using observations from Fall 2013 to improve 2011 AG5’s orbit has a 95% chance of eliminating the 2040 impact scenario, while further observations in 2015-2016 could drive that to ~99% eliminated.

• On the other hand, in the very unlikely case where the asteroid is actually on an Earth impacting trajectory, the 2013 observations could find the computed impact chance rising to 10% - 15%, and the observations in 2015 – 2016 could find it rising further, to ~70%. Only additional observations in 2013 and 2015 will increase the accuracy of these predictions.

• An impactor spacecraft could be an effective means of deflecting 2011 AG5 to avert an Earth collision. It is desirable to also have a rendezvous spacecraft on station at the asteroid at least a few months before the deflection in order to characterize the object, ease the targeting challenges for the impactor spacecraft, and to provide early confirmation of the magnitude of the deflection. This rendezvous spacecraft could be equipped with a gravity tractor capability as a backup to the impactor spacecraft.

• Many viable mission options exist for carrying out a pre-keyhole (before 2023) deflection campaign for 2011 AG5, using either chemical or solar electric propulsion (SEP) spacecraft, with launches in the 2018-2020 timeframe.

• Viable mission options also exist for carrying out a post-keyhole (after 2023) deflection using existing heavy lift launch vehicles and launch dates in the 2023 – 2030 timeframe.

• While much further study would be required to design optimal pre- and post- keyhole rendezvous and impact missions, this short study has demonstrated that numerous viable deflection mission options are available in the event that the 2011 AG5 is actually on a trajectory leading to a 2040 Earth impact.

• In the unlikely event that observations made in Fall 2013 show a significant increase in the Earth impact probability, there is still sufficient time to plan and carry out a successful deflection campaign.

From the NASA news release...

Researchers anticipate that asteroid 2011 AG5, discovered in January 2011, will fly safely past and not impact Earth in 2040.

Current findings and analysis data were reported at a May 29 workshop at NASA's Goddard Space Flight Center in Greenbelt, Md., attended by scientists and engineers from around the world. Discussions focused on observations of potentially hazardous asteroids (PHAs).

Observations to date indicate there is a slight chance that AG5 could impact Earth in 2040. Attendees expressed confidence that in the next four years, analysis of space and ground-based observations will show the likelihood of 2011 AG5 missing Earth to be greater than 99 percent.

Measuring approximately 460 feet (140 meters) in size, the space rock was discovered by the NASA-supported Catalina Sky Survey operated by the University of Arizona in Tucson. Several observatories monitored 2011 AG5 for nine months before it moved too far away and grew too faint to see.

"While there is general consensus there is only a very small chance that we could be dealing with a real impact scenario for this object, we will still be watchful and ready to take further action if additional observations indicate it is warranted," said Lindley Johnson, program executive for the Near-Earth Object (NEO) Observation Program at NASA Headquarters in Washington.

Several years ago another asteroid, named Apophis, was thought to pose a similar impact threat in 2036. Additional observations taken from 2005 through 2008 enabled NASA scientists to refine their understanding of the asteroid's path, which showed a significantly reduced likelihood of a hazardous encounter.

"Any time we're able to observe an asteroid and obtain new location data, we're able to refine our calculations of the asteroid's future path," said Don Yeomans, manager of NASA's NEO Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "When few observations exist, our initial orbit calculation will include a wider swath to account for uncertainties. With more data points, the knowledge of the potential positions of the asteroid improves and the swath becomes smaller -- typically eliminating the risk of an impact."

Observations of 2011 AG5 have been limited to date because of its present location beyond the orbit of Mars and in the daytime sky on the other side of the sun. In fall 2013, conditions will improve to allow space- and ground-based telescopes to better track the asteroid's path. At that time, 2011 AG5 will be 91 million miles (147 million kilometers) from Earth but favorably located for observations in the late evening sky.

The level of hazard will gain even more clarity in 2023, when the asteroid is approximately 1.1 million miles (1.8 million kilometers) from Earth. If 2011 AG5 passes through a 227-mile-wide (365-kilometer) region in space called a keyhole in early February 2023, Earth's gravitational pull could influence the object's orbital path just enough to bring it back for an impact on February 5, 2040. If the asteroid misses the keyhole, an impact in 2040 will not occur.

"Given our current understanding of this asteroid's orbit, there is only a very remote chance of this keyhole passage even occurring," said Johnson.

Although scientists widely expect it to be a safe flyby, they acknowledge the slight chance that computed odds could rise as a result of observations to be taken from 2013 to 2016. According to the experts at the workshop, even if the odds do increase, there is still ample time to plan and carry out at least one of several viable missions to change the asteroid's course.

PHAs are a subset of the larger group of near-Earth asteroids. They have the closest orbits to Earth's, coming within 5 million miles (about 8 million kilometers). They are large enough to enter Earth's atmosphere intact and cause damage on at least a local scale. Damage from an asteroid the size of 2011 AG5 could cover a region at least a hundred miles wide.

NASA established the NEO Program in 1998 to coordinate the agency's efforts to detect, track and characterize Earth-approaching NEOs and comets larger than 1 kilometer in size. The program now also searches for NEOs as small as object 2011 AG5. NASA supports NEO observation, tracking and analysis activities worldwide. Activities are coordinated through the NEO Program Office at JPL.

Link: NASA News Announcement

Link: NASA JPL NEO Page Annoucement

Link: NASA NEO JPL Links to Report
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