Researchers use radar to track near-Earth asteroids and predict hazards

Satellite image of the 1,000 foot radio telescope at Arecibo Observatory. Image Credit: GeoEye

Every year, UCLA graduate student Shantanu Naidu makes a pilgrimage to Arecibo Observatory, a uniquely constructed 300-meter radio telescope on the island of Puerto Rico.  His goal: to determine the shape, spin, orbit, and other physical properties of Near Earth Asteroids (NEAs).  These large chunks of rock left over from the formation of the solar system orbit around the Sun while remaining relatively close to Earth.

Observing asteroids with radio waves is a far cry from the traditional picture of nocturnal astronomers and mountaintop telescope domes housing fragile mirrors and lenses.  Since the wavelengths they employ are far outside the visible light spectrum, radar observations can take place as easily during the day as they can at night.  Likewise, the measurements are not affected by weather because the long wavelength radio waves can easily penetrate cloud layers in Earth’s atmosphere.
Naidu bounces radio waves off his targets and examines the reflected signal to reveal the shape of asteroids that would normally appear as “unresolved points of light” through optical telescopes.  Radio telescopes can both resolve and track these elusive objects.  Radar observations taken from Arecibo over the course of a few hours contain hundreds to thousands of pixels with surface resolutions as fine as 7.5 meters.

One of Naidu’s primary goals is to determine a precise orbit for each NEA he studies. At Arecibo, Naidu can pinpoint the position of an asteroid with an uncertainty of only a few tens of meters, a remarkable feat given that the majority of these objects are more than ten million kilometers from Earth.  The precision of an asteroid’s orbit is important because NEAs occasionally come close to Earth as they orbit around the Sun.  Scientists want to be able to identify any asteroid that could be a potential hazard decades or centuries before impact. “NASA wants to catalog the orbits of as many Near Earth Asteroids as possible so we can predict if any asteroid is going to collide with the Earth and take countermeasures,” said Naidu.  Radar measurements of NEAs enable Naidu and his colleagues to derive orbits for the objects far more accurately than any other method. With a single additional observation, the time interval for reliable trajectory predictions can be improved by a factor of 5 to 10, allowing scientists to chart the position of asteroids over the course of hundreds of years rather than decades.

Radar measurements help provide advanced warning for incoming asteroids, but only a tiny fraction of NEAs are currently being studied.  Naidu and his colleagues have observed roughly four hundred of these nearby asteroids, but scientists estimate that 20,000 NEAs with diameters greater than 100 meters exist in the solar system.

When Naidu observes an asteroid for the first time using radar, he hopes to hit the jackpot and see not just one object, but two or three.  What originally appears to be a single asteroid could instead be an asteroid binary, two asteroids that orbit each other like moons orbiting a planet.  “When we observe, we see that one in every six asteroids larger than 200 meters has a moon around it, so we know that binaries form a significant portion of the NEAs,” said Naidu.  “Fifteen years ago, we didn’t even know that binaries existed.”

Fourth-year graduate student Julia Fang works to model the “orbital architecture” of these complex multi-asteroid systems.  She creates computational models to predict how radiation from the Sun or a close encounter with the gravitational field of a planet could change the orbital paths of a multi-asteroid system.  She hopes to recreate the history of these complicated systems in order to understand what processes might be responsible for producing their current orbits.  “Asteroids provide clues about the orbital history of the planets and how they evolved,” said Fang.

Both Naidu and Fang are advised by UCLA Professor Jean-Luc Margot, one of the world’s foremost experts in high-precision radar observations of asteroids.  Additional information about the UCLA radar program is available at:

Learn more about Jean-Luc Margot’s research here.

Researchers analyze extrasolar asteroids using light from distant stars

An artist interpretation of an asteroid being broken apart. Image Credit: NASA/JPL/Caltech


When a Sun-like star reaches the end of its lifetime, it blows off its outer layers in a sustained stellar windstorm, leaving behind an Earth-sized, ultra-dense “white dwarf” star.  Astronomers thought they knew what to expect from these celestial leftovers, but were puzzled over a decade ago when they found that a large fraction of observed white dwarfs emit more infrared light than predicted.  Most white dwarf stars are composed of hydrogen and helium, but spectral measurements of some stars revealed puzzling signals from heavier elements such as calcium.

To UCLA Professor Michael Jura, the presence of additional elements indicated that the stellar atmospheres of these white dwarf stars were contaminated from an outside source.  Many scientists hypothesized that the interstellar medium, a cosmic soup of stray particles inhabiting the space between stars, was responsible for this stellar pollution.  Jura thought the answer might instead lie with extrasolar asteroids.  “It was a mystery.  A number of these stars had been known for quite a few years, but nobody knew quite why they were polluted,” he said.  Jura believes that the stellar contamination occurs when an asteroid perturbed out of its normal orbit plummets towards its parent star and is violently ripped to shreds by gravitational forces.  Starlight from the white dwarf is consequently absorbed by the newly created disk of dust and debris left over from the shattered asteroid.  The dusty ring encircling the star re-radiates the starlight as infrared light that is invisible to the human eye but can be measured by specialized telescopes on Earth.

The swirling cloud made from atomized asteroids does more than absorb light; it eventually becomes part of the star itself.  “What is particularly important is that this disk doesn’t just orbit the star, but that it slowly accretes onto the star,” said Jura.  Bits of asteroid falling into the white dwarf star contaminate the stellar atmosphere with heavier elements that wouldn’t ordinarily be present.  “Because we have these dust disks which are broken-up asteroids, we have a tool for measuring the elemental composition of extrasolar asteroids,” he said.

To figure out what these asteroids were made of before they were destroyed, Jura and his graduate student Siyi Xu use data taken from the Hubble and Spitzer space telescopes.  They also observe using the Keck telescopes on the big island of Hawaii a few nights every year.  So far, they have detected 19 different elements heavier than helium in their white dwarf measurements.

“We find the compositions of extrasolar asteroids are quite similar to meteorites in our own solar system. For one particular star, GD 362, the best match is mesosiderite, a type of stony-iron meteorite,” said Xu.  Oddly enough, Xu is able to measure traces of certain elements in meteorites vaporized by distant stars more easily than scientists studying intact meteorites in their labs.  “It is very hard to measure the bulk composition of a meteorite in a lab without destroying it completely,” Xu said.  “Since the asteroid is already broken up for us, we can measure all of the abundances and make a comparison.”

Determining the composition of extrasolar asteroids may help scientists understand how Earth-like exoplanets around stars are formed.  “We picture that when rocky planets form, they build up from nearby chunks of orbiting rock and debris,” Jura said.  “In our own solar system, that process was somewhat inefficient, so we have asteroids left over.”  Our solar system is one of many planetary systems with surplus building blocks left behind from planet formation; scientists estimate that nearly 30% of white dwarf star systems have extrasolar asteroid populations.

Previously, astronomers have only been able to guess the composition of asteroids in other star systems based on what they have learned about asteroids closer to home.  “We think they are probably the original suite of asteroids that formed when the star was forming planets,” Jura said.  “It’s just plain fun to think that you can actually figure out what these other planetary systems are made out of.”

Watch a video profile of Mike Jura here.  Learn more about his research here.

Watch a video profile of Siyi Xu here.

UCLA scientists monitor collisions in space

In a paper published in the Journal of Meteoritics and Planetary Science, UCLA Professor Christopher T. Russell and graduate student Hairong Lai present a new way of monitoring collisions between asteroids and meteroids.  Their method, developed based on 30 years of observational data on these small interplanetary objects, may help scientists better predict when debris from these impacts may pose a danger to Earth.

Read more about this recent discovery at: .

Professor Russell recently celebrated his seventieth birthday.  A two-day symposium was held May 8-9 to honor his long career in planetary science.