In four more days, on May 8th, 2016, a near earth object (NEO), 2013 TX68, will swing by earth. Scientists originally calculated this asteroid could possibly fly in an orbital trajectory between geosynchronous satellites and earth. That would be close. However, NASA scientists are now more confident with an updated orbital trajectory NEO passing five million km from earth.
“Asteroid 2013 TX68 is estimated to be about 100 feet (30 meters) in diameter. By comparison, the asteroid that broke up in the atmosphere over Chelyabinsk, Russia, three years ago was approximately 65 feet (20 meters) wide. If an asteroid the size of 2013 TX68 were to enter Earth’s atmosphere, it would likely produce an air burst with about twice the energy of the Chelyabinsk event.” according to NASA JPL.
A more recent asteroid trajectory estimate from “NASA, said the asteroid poses no threat to Earth. In fact, it’s ‘believed’ that the 2013 TX68 won’t come any closer than five million km from Earth. Initial estimates had the asteroid passing between 14 million, and 17,000 km. There is still a small chance that it will fly about 24,000 km above Earth,” according to Global News Network. This distance is of interest, because the moon is estimated to be: “363,104 km from earth,” so if the asteroid passes at 24,000 kilometers, then the asteroid pass would be approximately 15 times closer to earth than the lunar orbit. Geostationary orbit of satellites are roughly 35,786 km from earth. However, NASA currently expects (with more confidence), the asteroid will pass at a distance of 5,000,000 km from earth. There is still decreasing uncertainty, with the 2013 TX68 asteroid trajectory estimate also plausibly passing inside geostationary satellite orbits, at distance around 11,000km closer to earth than existing geostationary satellites.
The way to view astronomers changing estimates, is that probability estimates evolve over time. For example, astronomers may have placed the initial odds at 50% for a NEO pass of greater than 5,000,000 km, and 50% odds of a NEO pass around 24,000 km. Whereas now, with better resolution and better accuracy, scientists may estimate the odds to be 75% probability that a pass will now be greater than 5,000,000 km from earth, and only 25% uncertain probability the NEO would pass at around 24,000 km from earth, respectively.
What has been disconcerting for near earth asteroid trackers, in countries around the world, is the uncertainty about predictions within a week from a NEO encounter, especially with a newly discovered asteroid, where scientists have no previous orbital data for comparison.
Observations of rate, time, and distance get more precise as an asteroid closes within several days of passing by earth. However, this is not an ideal timeline to finally get accurate in orbital trajectory precision, as several days before an asteroid event, leaves little time for earth planners to respond, if a small asteroid becomes an impact hazard. However, as mentioned previously, NASA is now virtually certain 2013 TX68 will take the wider path by earth in four days. That is good news.
Some scientific minded persons may be skeptical, or annoyed with NASA for not knowing exactly where an asteroid is located in orbit, weeks ahead of time. Part of the reason for varied orbital estimates by NASA and others, is that asteroid tracking systems, such as space telescopes, get a very small object to calculate rate, time, and distance (against a fairly noisy interstellar background).
If a satellite image is captured from a satellite telescope, there can be limits to the object’s luminosity (brightness or lack of brightness), resulting in viewing a seemingly dark object against a dark background. Conversely, some asteroids travel around the sun in an opposite orbit towards earth. In this case, a high background luminosity (brightness) of intense sunlight obscures tiny objects in the foreground, when views from space satellites or earth observatories. In some cases, a NEO asteroid is so small and fast, like 2013 TX68, that for awhile, astronomers loose sight of the super small object against the hot white brilliance of the enormously larger sunlit background view. In more simple terms, if you focused a telescope on the sun, the light is so intense it has to be filtered through a dark lens just so a camera can film the sun, and a 30 meter rock millions of miles from earth against a super lit background, makes telescope tracking practically invisible, for a period of time, as the object continues to travel towards earth.
While NASA JPL and other nation’s observatories do a remarkable job, keeping an eye on the sky, they all miss a few asteroids due to small size, trajectory, and optical noise.
According to NASA this year, the U.S. Government chartered a Department of Planetary Defense, with a mission to identify asteroid threats, and to identify ways to mitigate threats of close encounters. That is real progress.