Skull-shaped Halloween close fly-by object is likely a dead comet

The large space rock that will zip past Earth this Halloween is most likely a dead comet that, fittingly, bears an eerie resemblance to a skull.

Scientists observing asteroid 2015 TB₁₄₅ with NASA’s Infrared Telescope Facility (IRTF) on Maunakea, Hawaii, have determined that the celestial object is more than likely a dead comet that has shed its volatiles after numerous passes around the Sun.

The belated comet has also been observed by optical and radar observatories around the world, providing even more data, including our first close-up views of its surface. Asteroid 2015 TB₁₄₅ will safely fly by our planet at just under 1.3 lunar distances, or about 302,000 miles (486,000 kilometres), today (31 October) at 17:00 UTC (~5pm GMT).

The first radar images of the dead comet were generated by the National Science Foundation’s 305-metre (1,000-foot) Arecibo Observatory in Puerto Rico. The radar images from Arecibo indicate the object is spherical in shape and approximately 2,000 feet (600 metres) in diameter and completes a rotation about once every five hours.

“The IRTF data may indicate that the object might be a dead comet, but in the Arecibo images it appears to have donned a skull costume for its Halloween flyby,” said Kelly Fast, IRTF program scientist at NASA Headquarters and acting program manager for NASA’s NEO Observations Program.

Managed by the University of Hawaii for NASA, the IRTF’s 3-metre (10 foot) telescope collected infrared data on the object. The data may finally put to rest the debate over whether 2015 TB₁₄₅, with its unusual orbit, is an asteroid or is of cometary origin.

“We found that the object reflects about six percent of the light it receives from the Sun,” said Vishnu Reddy, a research scientist at the Planetary Science Institute, Tucson, Arizona. “That is similar to fresh asphalt, and while here on Earth we think that is pretty dark, it is brighter than a typical comet which reflects only 3 to 5 percent of the light. That suggests it could be cometary in origin — but as there is no coma evident, the conclusion is it is a dead comet.”

Asteroid 2015 TB₁₄₅ was discovered on 10 October 2015, by the University of Hawaii’s Pan-STARRS-1 (Panoramic Survey Telescope and Rapid Response System) on Haleakala, Maui, part of the NASA-funded Near-Earth Object Observations (NEOO) Program. The next time the asteroid will be in Earth’s neighbourhood will be in September 2018, when it will make a distant pass at about 24 million miles (38 million kilometres), or about a quarter the distance between Earth and the Sun.

Radar is a powerful technique for studying an asteroid’s size, shape, rotation, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than would be possible otherwise.

Observing 2015 TB₁₄₅ from the UK on Saturday evening

For observers in the British Isles with a clear sky low to the north-northwest in deep twilight on 31 October, there is a chance to see this fascinating asteroid/comet as it passes just under one degree (57 arcminutes) south of magnitude +2.4 star gamma (γ) Ursae Majoris, otherwise known as Phad, the lower-left star in the bowl of the Big Dipper, at 18:08 UT (~6:08pm GMT). According to predictions, 2015 TB₁₄₅ should be about magnitude +11.2 and therefore visible in 6-inch telescopes or larger. At this time the object is travelling at almost 13 degrees/hour with respect to the background stars, so the motion of 2015 TB₁₄₅ will be evident in realtime in large ‘scopes. For observers with computerised GoTo mounts, here are the J2000.0 epoch topocentric coordinates of the object for the centre of the UK.