Note: Asteroid 2004 NM4 has been named 99942 Apophis, where Apophis or Apep was an ancient Egyptian god of evil, destruction and darkness. Dave Tholen at University of Hawaii explains this name: "It is traditional to name Aten-class asteroids after Egyptian gods. While it is an Aten-class object now, MN4 will become an Apollo-class asteroid after the 2029 close approach, and Apollo-class asteroids have traditionally been named after Greek gods. So we selected the Greek name for an Egyptian god. Apophis is the Greek name for the Egyptian god Apep, the god of evil and destruction. Apep was usually thwarted in his destructive efforts, however. Apophis isn't going to get us, at least this time around".
Last December, asteroid Apophis (2004 MN4) briefly rose to Torino Scale 4, when orbital calculations suggested a greater than 1 in 50 chance of collision on April 13, 2029. Subsequent optical and radar observations showed that Apophis will not collide with Earth in 2029, but it will come very close (see "Asteroid MN4 and How to Protect the Earth" in the News Archive for April 25, 2005). Current interest (and concern) is directed at possible future impacts, if Apophis should pass through a "keyhole" in 2029 and find itself in a resonant orbit (such as one in which the asteroid makes exactly 6 orbits of the Sun in 7 years, returning to Earthıs vicinity every 7 years.) A keyhole is a small region of space that leads an asteroid back to hit Earth on subsequent encounters.
Based on current knowledge of the orbit of Apophis, we cannot exclude the possibility of it passing though a keyhole and hitting the Earth on a subsequent pass. However, there will be opportunities to make improved optical and radar observations, which are likely to confirm that it will miss the keyholes. It would also be possible to place a transponder on the asteroid and use this to verify whether or not it will pass through a keyhole in 2029. The issue is whether the ground-based orbital improvements will come in time to make a mission decision, or whether we need to plan for a transponder mission in any case.
Why the hurry? It is because if we should need to deflect the asteroid (which is unlikely but possible), our technology requires that the deflection take place before the close flyby in 2029. Before 2029 we only need to it enough to miss the keyholes (which are less than 1 km across). But if a deflection were required after 2029, it would have to be enough to miss the much larger target of the Earth itself, which is far beyond present technology for as asteroids this large.
Following is a communication from former Apollo astronaut Rusty Schweickart discussing these options.
To David Morrison (July 20, 2005)
Clark Chapman and I have just concluded a meeting at JPL with NASA's NEO folks pursuant to our letter to Administrator Mike Griffin (printed below). This was the kickoff to NASA's process of responding to the issues we raised in the letter. Our understanding is that NASA will complete its analysis of the issues and respond officially to us by the end of August. Based on our discussion, and without pre-judging the results of NASA's more detailed analysis, there are several key factors that will likely shape their conclusions. The first is the issue of the time required from decision to commit to a mission to completion of that mission. This "mission time" applies to both a deflection mission and a mission to emplace a transponder on the asteroid, should either mission be required. [Clark Chapman notes that "mission time" is used here to mean the total duration from beginning Phase A through completion of the mission. It thus includes development of the mission concept, building the spacecraft, launch, flight to MN4, and sufficient operation at the asteroid either to obtain reliable transponder observations (in the case of a transponder mission) or time to deflect and verify deflection].
If the mission time is as short as 6 years, then the decision of whether or not a transponder is needed to support a deflection decision can be delayed until 2014. This is a critical date because not only does optical tracking data become available again by that time, but there is also a good radar apparition in early 2014. If the decision on a transponder mission can await this date, the possibility that neither mission is required is much higher than if a decision must be made now. Our tentative conclusion that a decision must be made now is based on the far more pessimistic assumption that the mission time for a deflection mission might be as long as 12 years, and for a transponder mission 7-8 years. These assumptions, on which JPL is far more expert than we, led to the conclusion that a near-term decision on the transponder mission is required. We await NASA's analysis regarding the feasibility of sequential 6-year mission times. The second key issue is the joint realization that the uncertainties introduced by the Yarkovsky effect on this asteroid may well play a major role in the decision making. While the Yarkovsky effect is a relatively minor issue in the case of an asteroid headed for the 12,800-km-diameter Earth in 15 years, it is a major influence when the immediate target of the asteroid is a 600-meter-wide keyhole! Again, however, if the major mission decisions can be deferred until after the 2014 radar apparition, the influence of the Yarkovsky effect on this asteroid will be far better estimated. As we've always emphasized, the likely need for a deflection mission is very low, but it cannot be ignored or wished away. If a delay in the decision time can be safely deferred to 2014, the quality of information on which such a decision must be made will be materially higher. We await NASA's analysis of the many factors involved this decision process.
Rusty Schweickart Chairman, B612 Foundation
Letter to NASA Administrator Michael Griffin:
Dear Mr. Griffin:
I am writing this letter on behalf of the B612 Foundation and others to request your support in resolving an issue of critical importance. The issue is best stated as a question; is it desirable, or perhaps necessary, to launch a scientific mission to asteroid 2004MN4 in the near future, in order to have adequately accurate knowledge of its orbit in time to initiate a deflection mission in the unlikely event one should be needed?
As you know, near-Earth asteroid 2004MN4 is unique because of its unusually close pass by the Earth on April 13, 2029. Based on current data, the asteroid (320-400 meter diameter) will pass approximately 7,000 km inside the geostationary orbit and will be an easily visible naked eye object to observers in Europe and Africa early that evening. Because of this very close encounter, the orbit of the asteroid will be substantially altered as it passes Earth, resulting in a small probability that it will return in 2036 if it happens to pass through the most probable of several "keyholes" which lie within the current error ellipse.
While the probability of this event is very low (approximately 1 in 15,000 based on current data), the consequences of an impact are so high (> $400 billion of infrastructure loss alone) that this possibility warrants careful attention. Specifically, the size of the keyhole which must be avoided during the 2029 encounter is so small (~600 meters) that the best navigational data we will have, at the time we would have to decide on a deflection mission, will be inadequate to make that determination. This claim is based on the anticipated optical and radar tracking opportunities between now and 2014, when we believe a deflection mission would have to be initiated in order to assure a successful deflection.
The augmentation we propose to our ground tracking capability is the launch and subsequent docking of a scientific mission, including a standard radio transponder, with 2004MN4. While the improvement in our knowledge of the asteroidıs orbit would resolve the issue of a potential impact, the scientific knowledge gained of both the surface and interior characteristics of the asteroid would be invaluable for future operations in and of itself. The unique circumstance presented by this asteroid which might have to be deflected, whose size makes it probable that it has a "rubble pile" structure, and whose orbit will bring it within the range of distorting terrestrial tidal forces, makes this a very attractive learning opportunity.
We sincerely urge you to direct the NASA NEO Program resources to conduct a thorough and cooperative analysis of this issue.
Russell L. Schweickart
Chairman, Board of Directors