Since our last post in December, ATLAS operations have become smoother and more efficient. We have resolved a host of problems, improved our hardware significantly and our software enormously, and gained a great deal of experience managing our unique asteroid-detection system. We are now reporting asteroid discoveries from each night promptly in the morning, with the result that each new discovery gets followed up by other astronomers across the world on the following night. This is very important, since additional observations of a newly discovered asteroid are essential to calculate an accurate orbit and evaluate any impact hazards. Both amateur and professional observers in many nations routinely participate in this endeavor.
ATLAS has now discovered seven NEOs that received official designations from the Minor Planet Center: two in December, one each in January and February, and three so far in March. They range in size from little 2016 CS247, with a diameter of about 30 meters (100 feet), to 650 meter (2000 foot) 2016 BZ14. This last object came as a surprise: we would not have expected our little ATLAS telescope to catch an asteroid as large as 2016 BZ14 before any other survey. ATLAS is optimized for small objects passing very close to Earth, and surveys using bigger telescopes normally find all of the larger, more distant NEOs. However, 2016 BZ14 shows that on rare occasions a larger asteroid can slip through the cracks.
All of the ATLAS NEOs were big enough to be dangerous – even 2016 CS247 could have destroyed a medium-sized city – but thankfully all seven asteroids passed by Earth at a safe distance, and orbital calculations show that none will be a hazard for the foreseeable future.
Like their sizes, the orbits of ATLAS NEOs exhibit a wide range of properties that illustrate both the versatility of the ATLAS survey and the intrinsic diversity of the asteroid population. The figures below show the orbits of each new NEO in relation to Earth’s trajectory during the period surrounding the discovery. Earth’s orbit is the thick, pale-blue line, and its location on the night of the discovery corresponds to where this line crosses the x axis. The diamond symbols show the position of each asteroid when ATLAS discovered it. The first figure gives the view looking down on Earth from the direction of the North Ecliptic Pole. The second gives the view from the plane of the ecliptic. In both cases the Sun is out of view on the left, and the axes are labeled with distance in astronomical units (AU). It is easy to see that 2016 BZ14 was discovered much farther from the Earth than the other, smaller asteroids, which had to come closer before ATLAS could see them.