“The double asteroid was hurtling by the Earth at more than 70 000 km/h, making observing it with the Very Large Telescope (VLT ) challenging,” said Diego Parraguez, who was piloting the European Southern Observatory telescope. He had to use all his expertise to lock on to the fast asteroid and capture it with SPHERE, one of the very few instruments in the world capable of obtaining images sharp enough to distinguish the two components of the asteroid, which are separated by around 2.6 km.
Stephen Hawking believed that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets. We observed, Hawking points out in Life in the Universe, the collision of a comet, Schumacher-Levi, with Jupiter, which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot “bubbles” of gas in the atmosphere, and large dark “scars” on the atmosphere which had lifetimes on the order of weeks.
Through Earth’s history such collisions occur, on the average every one million year. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, Hawking believes, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.
“The threat of the Earth being hit by an asteroid is increasingly being accepted as the single greatest natural disaster hazard faced by humanity,” according to Nick Bailey of the University of Southampton’s School of Engineering Sciences team, who has developed a threat identifying program.
Back to the present: The International Asteroid Warning Network (IAWN) coordinated a cross-organizational observing campaign of the asteroid 1999 KW4 as it flew by Earth, reaching a minimum distance of 5.2 million km on 25 May 2019. 1999 KW4 is about 1.3 km wide, and does not pose any risk to Earth. Since its orbit is well known, scientists were able to predict this fly-by and prepare the observing campaign.
SPHERE was designed to observe exoplanets; its state-of-the-art adaptive optics (AO) system corrects for the turbulence of the atmosphere, delivering images as sharp as if the telescope were in space. It is also equipped with coronagraphs to dim the glare of bright stars, exposing faint orbiting exoplanets.
Taking a break from its usual night job hunting exoplanets, SPHERE data helped astronomers characterize the double asteroid. In particular, it is now possible to measure whether the smaller satellite has the same composition as the larger object.
“These data, combined with all those that are obtained on other telescopes through the IAWN campaign, will be essential for evaluating effective deflection strategies in the event that an asteroid was found to be on a collision course with Earth,” explained ESO astronomer Olivier Hainaut. “In the worst possible case, this knowledge is also essential to predict how an asteroid could interact with the atmosphere and Earth’s surface, allowing us to mitigate damage in the event of a collision.”
Bin Yang, VLT astronomer, declared “When we saw the satellite in the AO-corrected images, we were extremely thrilled. At that moment, we felt that all the pain, all the efforts were worth it.” Mathias Jones, another VLT astronomer involved in these observations, elaborated on the difficulties. “During the observations the atmospheric conditions were a bit unstable. In addition, the asteroid was relatively faint and moving very fast in the sky, making these observations particularly challenging, and causing the AO system to crash several times. It was great to see our hard work pay off despite the difficulties!”
While 1999 KW4 is not an impact threat, it bears a striking resemblance to another binary asteroid system called Didymos which could pose a threat to Earth sometime in the distant future.
Didymos and its companion called “Didymoon” are the target of a future pioneering planetary defence experiment. NASA’s DART spacecraft will impact Didymoon in an attempt to change its orbit around its larger twin, in a test of the feasibility of deflecting asteroids. After the impact, ESA’s Hera mission will survey the Didymos asteroids in 2026 to gather key information, including Didymoon’s mass, its surface properties and the shape of the DART crater.
The success of such missions depends on collaborations between organizations, and tracking Near-Earth Objects is a major focus for the collaboration between ESO and ESA. This cooperative effort has been ongoing since their first successful tracking of a potentially hazardous NEO in early 2014.
“We are delighted to be playing a role in keeping Earth safe from asteroids,” said Xavier Barcons, ESO’s Director General. “As well as employing the sophisticated capabilities of the VLT, we are working with ESA to create prototypes for a large network to take asteroid detection, tracking and characterization to the next level.”
This recent close encounter with 1999 KW4 comes just a month before Asteroid Day, an official United Nations day of education and awareness about asteroids, to be celebrated on 30 June. Events will be held on five continents, and ESO will be among the major astronomical organizations taking part. The ESO Supernova Planetarium & Visitor Centre will host a range of activities on the theme of asteroids on the day, and members of the public are invited to join in the celebrations.
The Daily Galaxy, Jake Burba, via ESO