Are you worried about an asteroid, meteorite or comet hitting the Earth hard enough to do some deadly damage? Do you feel better or worse when you learn that there are over 29,000 known near-Earth asteroids (NEAs) and over a hundred known short-period near-Earth comets (NECs) that could become potentially hazardous objects (PHOs)? Did you change your mind after NASA hit a tiny rock orbiting a slightly bigger rock with a rocket that slightly altered its orbit? While the DART mission was an impressive feat, the emphasis should be on “tiny” and the fact that neither were posing any danger to Earth. On the other hand, astronomers recently noticed that one of the largest asteroids in the asteroid belt – one that has already been identified as a near-Earth asteroid and a potentially hazardous object – just changed its rotation for no apparent reason. Is it getting ready to make a move towards Earth? How much destruction could a 5.4 kilometer in diameter asteroid do? Do we need a bigger DART? A SPEAR? How about a DEATH STAR? NOW are you worried?
“A team of scientists led by Arecibo Observatory and the University of Central Florida has measured a change in the rotation period of the potentially hazardous near-Earth asteroid 3200 Phaethon, a future spacecraft target. Phaethon is just the 11th asteroid with a measured change in its rotation period, and it is the largest of them.”
Wishful thinking would have those sentences as the opening lines of a dystopian ‘We’re all gonna die when that giant asteroid hits!’ movie, but they are actually the introduction to a press release from astronomers at the University of Central Florida and the Arecibo Observatory (it is nice to see that the Arecibo Observatory is still functioning even after its famed telescope had to be demolished) have detected a change in the rotation period of 3200 Phaethon. While not the Aaron Judge of monster asteroids, it is in the top tier of terrifying space rocks – scary and dangerous enough to potentially live up to its Greek mythology name. Phaethon was the son of the sun god Helios, who begged his father to let him drive the family chariot (the one representing the sun), only to take the reins and drive it too close to the Earth, creating so much havoc that Zeus kills him with a lightning bolt. Now we have the real, already dangerous Phaeton changing its rotation. Should we be worried? Is it too late? The astronomers announced the 3200 Phaeton news at the 54th annual meeting of the American Astronomical Society’s Division for Planetary Sciences.
“Phaethon rotates once every 3.6 hours, and that rotation period is decreasing by about 4 milliseconds per year. The next-largest asteroid with a measured change in its rotation period is near-Earth asteroid 1685 Toro, with a diameter of about 3.5 kilometers.”
The asteroid that created the Chicxlub crater and exterminated the dinosaurs measured 6.2 miles (10 km) in diameter – about twice the diameter of 3200 Phaethon. Needless to say, it could still pack a punch, which is one reason why it has been under close observation by astronomers since its discover in 1983 by Simon F. Green and John K. Davies while searching Infrared Astronomical Satellite (IRAS) data for moving objects. 3200 Phaethon has an orbit that brings it closer to the Sun than any other named asteroid, allowing it to be closely observed using optical light curves, showing variations in its brightness as it rotates, radar from NASA’s Goldstone Deep Space Communications Complex, and stellar occulations. Phaethon was 18,085,600 km (11,237,900 mi) from Earth on December 10, 2007, and its perihelion in July 2009 was brighter than expected. On December 16, 2017, it passed closer -- 10,312,034 km or 6,407,601 miles – and was visible with small telescopes. Its next pass comes in 2093 and will e even closer -- 2,964,000 km or 1,841,000 miles. However, that calculation was made before its rotation changed. Should we start getting worried and building a bigger DART?
“Due to its interesting characteristics, the Japanese Aerospace Exploration Agency (JAXA) selected Phaethon as the target of the upcoming DESTINY+ mission, which is scheduled to launch in 2024 and fly by Phaethon in 2028. The DESTINY+ mission’s objectives are to make observations of Phaethon and interplanetary dust and to demonstrate technologies for deep space exploration.”
The bad news is … we don’t know for sure. The good news is … some farsighted astronomers at the Japanese space agency JAXA have been planning a mission to 3200 Phaeton and it should be ready for launch in 2024. DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary voYage Phaethon fLyby dUSt science) is supposed to get within 310 miles (500 km_ of 3200 Phaeton, according to Arecibo planetary scientist Sean Marshall, who says that will be close enough to determine the size, shape and rotation state of Phaethon. Should NASA join with JAXA and equip DESTINY+ with a DART (Double Asteroid Redirection Test) just in case?
“The investigation team has confirmed the spacecraft’s impact altered Dimorphos’ orbit around Didymos by 32 minutes, shortening the 11 hour and 55-minute orbit to 11 hours and 23 minutes. This measurement has a margin of uncertainty of approximately plus or minus 2 minutes.”
NASA confirmed last week that DART had indeed altered the orbit of Dimorphos around Didymos – an impressive accomplishment and a positive step towards protecting Earth from killer asteroids. Except … Dimorphos was no killer asteroid – it measures just 170 meters (560 feet) across; Didymos isn’t much bigger at 832 meters (.5 miles) in diameter. The DART spacecraft would pose no threat to 3200 Phaethon. Does 3200 Phaethon now pose a danger to Earth?
Probably not. That is good news for fans of the Geminids meteor shower – that annual December event is caused by Phaethon … one of only two asteroids to be the parent of a meteor shower (the Quadrantids are the others). Still, Phaethon is an anomaly to astronomers --- the amount of debris it generates is highly unusual for its size. Then there is that mysterious rotational change. Should astronomers be as complacent as they seem to be about the potential danger of near Earth asteroid and potentially hazardous object 3200 Phaethon?
What would Bruce Willis do? Leonardo DiCaprio?