Earth's Date With an Asteroid

Scientists at the University of Arizona have had a long love with rocks whizzing through space, and the record-setting asteroid hurtling toward the Earth before veering off into space on Feb. 15 is no different.

No asteroid of this size – half a football field across – has been known to make such a close pass since record-keeping observations began in the 1990s, according to Don Yeomans of NASA’s Near-Earth-Object Observation Program at the Jet Propulsion Laboratory in Pasadena, Calif.

The stony asteroid, 2012 DA14, likely originated in the solar system’s asteroid belt between Mars and Jupiter. It will pass Earth at a distance of about 17,200 miles or 27,680 kilometers, closer than geostationary satellite orbit, although experts consider a crash extremely unlikely.

"As we keep getting better at finding these things, we discover that such close approaches happens more frequently than you might think," said Ed Beshore, deputy principal investigator of the UA’s OSIRIS-REx mission, which will send a spacecraft to an asteroid, scoop up a sample and bring it back to Earth for study.

Although the "Valentine asteroid" definitely won't impact our planet this time, it serves as a reminder that such Near-Earth Objects, or NEOs, have slammed into the Earth in the past and will do so in the future. Yeomans said an object the size of DA14 streaks down from the sky about every 1,200 years on average.

"NEOs are obviously special because they are hazards to Earth," Beshore said. "Over the long term, NEOs either collide with the sun or a planet, or get thrown out of the solar system by a close gravitational approach."

"Something is responsible for resupplying the solar system with these objects, and this is the subject of much study," he added. "Collision threat aside, NEOs are scientifically interesting – their close approaches to Earth afford excellent opportunities to study them in detail."

Observing campaigns will study the asteroid with various instruments including NASA’s Goldstone radio telescope in California. From these observations, scientists will learn more about its orbit, rotation and physical characteristics.

"It's not often that we get to observe such a small asteroid at close range," said Carl Hergenrother, OSIRIS-REx Science Team member and coordinator of the Target Asteroids! citizen science program. "This object is small and fast but relatively bright – it offers professionals and amateurs a great chance to collect data and test their observing skills. I will be on the Vatican Advanced Technology Telescope the night of the close approach obtaining light curve and color observations."

"Right now, we have about a 100-year window of certainty of not getting hit by any NEO we have discovered to date," Beshore said. "Beyond that, we can’t say what the long-term future holds for these objects. It is in everybody’s interest to improve our ability to predict their behavior."

Through repeated and concerted observations, professional and amateur astronomers alike are continually refining the orbits of asteroids, he said.

"One of the best things we can do is get radar images," he added. "They allow us to measure an asteroid's distance to within a few tens of feet, which is not possible to do with optical instruments. Radar images also allow us to map these rocks, giving us an idea of what they look like. What shape are they? Is their surface smooth or covered with boulders? How fast are they rotating?"

"The goal is to lengthen that window out farther into the future."

An important piece in this effort is NASA’s OSIRIS-REx mission, led by the UA, even long before it embarks on its journey to its target asteroid, 1999 RQ36. While the major scientific objective of the mission is to bring back a sample of the asteroid for study here on Earth, OSIRIS-REx scientists are also working to understand a phenomenon that applies to all asteroids, large or small, called the Yarkovsky effect.

As an asteroid travels along its orbit, it absorbs light and heat from the sun. As it rotates, it radiates some of that energy back into space. Over time, this re-radiated energy nudges the object off its trajectory ever so slightly, making its course more difficult to predict, especially over long timespans into the future.

"By observing asteroid RQ36 from Earth, we have already obtained a much better understanding of the Yarkovsky effect. We hope to refine our measurements as part of the OSIRIS-REx mission and improve our orbital predictions, even for asteroids that are slightly different in size or composition," Beshore explained. "With the data, we expect to refine our computer simulations and make them more accurate."

A close encounter like that of DA14 puts observers in a prime seat to follow the space rock as it interacts with Earth. As the asteroid races toward Earth from the south and streaks high across the Indian Ocean, the Earth’s gravitational field grabs it and flings it off into space in a so-called gravitational slingshot.

According to Beshore, objects larger than about 0.6 miles (1 kilometer) are still being discovered, even though much less frequently than only seven or eight years ago.

"NASA is developing concepts to improve our sensitivity so we can detect objects that are smaller, further away, or both."

Scientists at the UA started looking for asteroids before NASA did. SPACEWATCH and Catalina Sky Survey are two research programs at the UA's Lunar and Planetary Laboratory dedicated to the study of small objects like asteroids and comets. Founded in 1980 by the late Tom Gehrels and Robert McMillan, who is now its principal investigator, SPACEWATCH aims to find objects that might pose a hazard to Earth and gain a better understanding of how the solar system came to be.

The Catalina Sky Survey, begun and led by LPL senior staff scientist Steve Larson, is a NASA-supported project to discover and catalog Earth-approaching and potentially hazardous asteroids.

"In more recent years, the UA’s Catalina Sky Survey has taken a leading role in discovering these objects, and now we're sending a spacecraft under the OSIRIS-REx mission," said Beshore, who directed the survey from 2009 to early 2012.

DA14 is about one-tenth the size of asteroid 1999 RQ36, which the OSIRIS-REx mission will visit in 2018 and from which it will return a sample to Earth in 2023.

Dante Lauretta, principal investigator for the OSIRIS-REx mission, believes 1999 RQ36 may hold important clues to the formation of the solar system.

"We think 1999 RQ36 is a primitive object, relatively unchanged since the beginning of the solar system. The chance to examine a sample in laboratories here on Earth may lend important clues to the source of organic materials and water – both critical to our understanding of how life arose on Earth, and the prospects for finding it elsewhere."

Furthermore, OSIRIS-REx will be a pathfinder mission, Lauretta said, helping us understand the techniques and technologies needed to navigate and work in an asteroid’s microgravity environment – important preparation for dealing with a future hazard or preparing for a manned expedition to an asteroid some day.