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Why We Track Asteroids Like the One That Flew by This Week

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Earlier this week, on March 8, asteroid 2013 TX68 came within about 3.1 million miles of Earth, astronomers estimate. Original predictions suggested its closest approach might be within the orbits of geostationary satellites around the Earth, or it could be as far away as 9.5 million miles. Additional data changed the distance range to between 3 million and 15,000 miles. At about 100 feet in diameter, the object was too small to be seen at the 3.1 million-mile distance, but it clearly did not hit Earth.

We keep an eye on such space debris. NASA’s Center for Near-Earth Object Studies at the Jet Propulsion Laboratory in California currently tracks 13,947 near-Earth objects, defined as those coming within 130 million miles of our planet’s orbit. The center considers about 12 percent of those potentially hazardous, according to Paul Chodas, manager of the center. That means they come within 5 million miles and pose about a one in 1 billion chance of hitting Earth in the next 100 years. (TX68 isn’t one of them.)

Asteroids travel on elliptical orbits around the Sun, explains Judit Györgyey Ries, an asteroid observer and researcher at the University of Texas at Austin’s McDonald Observatory. An asteroid’s path changes slightly from the effect of gravity when it passes close to a planet or from the energy of it absorbing and emitting sunlight.

The orbit of asteroid TX68. Image credit: NASA/JPL-Caltech

The more data scientists collect on a specific asteroid, the more accurate their predictions of its path and probability of colliding with Earth. TX68 is a perfect example. It was first observed by the Catalina Sky Survey in October 2013, while approaching Earth at night. Three days later, the asteroid passed into the daytime sky and could no longer be observed. Based on those three days of data, TX68 appeared to have a four in 1 billion chance of hitting Earth.

That may sound like a long shot, but the odds were nevertheless four times higher than the threshold NASA has set for potentially hazardous objects. “That caught our attention,” Chodas says. Then Italian astronomer Marco Micheli, with the European Space Agency, noticed faint traces of the asteroid in archived telescope images, which directed a search for more archived images. Based on that additional data, TX68’s potential for impact dropped back to the more acceptable one-in-a-billion chance.

All calculations come with uncertainty, of course, and with asteroids, that uncertainty grows the farther into the future the orbit projection. At the scale of the Earth, this uncertainty equals large distances, on the order of millions of miles. (For perspective, the average distance from Earth to the Moon is about 239,000 miles.) That makes it important for scientists to continue to monitor known objects.

Now scientists know where to look for TX68 when it returns to our part of the solar system. If it turns up where expected, that will decrease uncertainty about its future orbit. If not, says Györgyey Ries, the uncertainty will grow.

Three years ago, a meteor about 60 feet wide broke up in the atmosphere over Chelyabinsk, Russia. Observers didn’t see it coming because of its small size and approach from the direction of the Sun, but the dashcam and smartphone recordings of its fiery descent and glass-shattering sound wave were subsequently seen worldwide.

Any object between about 100 and 165 feet should burn up and disintegrate in the atmosphere, Chodas says, with some small meteorites reaching the ground, as they did in Chelyabinsk. NASA mostly worries about roughly 1000 known objects measuring at least one kilometer, or about six-tenths of a mile.

NASA-funded surveys began scanning the night sky in 1998 for near-Earth objects, and about 1500 NEOs are now detected each year. The strategy, according to Chodas, is to find as many of these objects measuring 330 feet and larger as possible, to provide as much time as possible for attempts to deflect a potential impact. For example, preparations for diverting a large asteroid of 650 to 1000 feet might involve building and launching a rocket, which would take years.

“You would just have to nudge it,” Chodas says. “Presumably, we could launch as heavy a rocket as we possibly could to run into the asteroid and change its velocity slightly. A change of one meter per second would likely be enough to divert it from impact.” NASA has plans for two missions to test deflection methods.

In January, NASA announced that its NEO detection and tracking project, now called the Planetary Defense Coordination Office, will supervise all NASA-funded projects working to find and characterize asteroids and comets passing near Earth's orbit and also coordinate response to potential impact threats.

For Chodas, TX68’s fly by presented an opportunity. “We know this particular asteroid can’t impact Earth in the next 100 years,” he says. “It is more of an opportunity to remind people we are working on the problem so that, if an asteroid should be headed for Earth, we would have enough warning time, possibly decades, to do something about it.”

But as Györgyey Ries notes, “I only worry about the ones we don’t know of.” 

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Look Up! Residents of Maine and Michigan Might Catch a Glimpse of the Northern Lights Tonight
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The aurora borealis, a celestial show usually reserved for spectators near the arctic circle, could potentially appear over parts of the continental U.S. on the night of February 15. As Newsweek reports, a solar storm is on track to illuminate the skies above Maine and Michigan.

The Northern Lights (and the Southern Lights) are caused by electrons from the sun colliding with gases in the Earth’s atmosphere. The solar particles transfer some of their energy to oxygen and nitrogen molecules on contact, and as these excited molecules settle back to their normal states they release light particles. The results are glowing waves of blue, green, purple, and pink light creating a spectacle for viewers on Earth.

The more solar particles pelt the atmosphere, the more vivid these lights become. Following a moderate solar flare that burst from the sun on Monday, the NOAA Space Weather Prediction Center forecast a solar light show for tonight. While the Northern Lights are most visible from higher latitudes where the planet’s magnetic field is strongest, northern states are occasionally treated to a view. This is because the magnetic North Pole is closer to the U.S. than the geographic North Pole.

This Thursday night into Friday morning is expected to be one of those occasions. To catch a glimpse of the phenomena from your backyard, wait for the sun to go down and look toward the sky. People living in places with little cloud cover and light pollution will have the best chance of spotting it.

[h/t Newsweek]

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Kevin Gill, Flickr // CC BY-2.0
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10 Facts About the Dwarf Planet Haumea
Kevin Gill, Flickr // CC BY-2.0
Kevin Gill, Flickr // CC BY-2.0

In terms of sheer weirdness, few objects in the solar system can compete with the dwarf planet Haumea. It has a strange shape, unusual brightness, two moons, and a wild rotation. Its unique features, however, can tell astronomers a lot about the formation of the solar system and the chaotic early years that characterized it. Here are a few things you need to know about Haumea, the tiny world beyond Neptune.

1. THREE HAUMEAS COULD FIT SIDE BY SIDE IN EARTH.

Haumea is a trans-Neptunian object; its orbit, in other words, is beyond that of the farthest ice giant in the solar system. Its discovery was reported to the International Astronomical Union in 2005, and its status as a dwarf planet—the fifth, after Ceres, Eris, Makemake, and Pluto—was made official three years later. Dwarf planets have the mass of a planet and have achieved hydrostatic equilibrium (i.e., they're round), but have not "cleared their neighborhoods" (meaning their gravity is not dominant in their orbit). Haumea is notable for the large amount of water ice on its surface, and for its size: Only Pluto and Eris are larger in the trans-Neptunian region, and Pluto only slightly, with a 1475-mile diameter versus Haumea's 1442-mile diameter. That means three Haumeas could fit sit by side in Earth—and yet it only has 1/1400th of the mass of our planet.

2. HAUMEA'S DISCOVERY WAS CONTROVERSIAL.

There is some disagreement over who discovered Haumea. A team of astronomers at the Sierra Nevada Observatory in Spain first reported its discovery to the Minor Planet Center of the International Astronomical Union on July 27, 2005. A team led by Mike Brown from the Palomar Observatory in California had discovered the object earlier, but had not reported their results, waiting to develop the science and present it at a conference. They later discovered that their files had been accessed by the Spanish team the night before the announcement was made. The Spanish team says that, yes, they did run across those files, having found them in a Google search before making their report to the Minor Planet Center, but that it was happenstance—the result of due diligence to make sure the object had never been reported. In the end, the IAU gave credit for the discovery to the Spanish team—but used the name proposed by the Caltech team.

3. IT'S NAMED FOR A HAWAIIAN GODDESS.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was proposed by the astronomers at Caltech to honor the place where Haumea's moon was discovered: the Keck Observatory on Mauna Kea, Hawaii. Its moons—Hi'iaka and Namaka—are named for two of Haumea's children.

4. HAUMEA HAS RINGS—AND THAT'S STRANGE.

Haumea is the farthest known object in the solar system to possess a ring system. This discovery was recently published in the journal Nature. But why does it have rings? And how? "It is not entirely clear to us yet," says lead author Jose-Luis Ortiz, a researcher at the Institute of Astrophysics of Andalusia and leader of the Spanish team of astronomers who discovered Haumea.

5. HAUMEA'S SURFACE IS EXTREMELY BRIGHT.

In addition to being extremely fast, oddly shaped, and ringed, Haumea is very bright. This brightness is a result of the dwarf planet's composition. On the inside, it's rocky. On the outside, it is covered by a thin film of crystalline water ice [PDF]—the same kind of ice that's in your freezer. That gives Haumea a high albedo, or reflectiveness. It's about as bright as a snow-covered frozen lake on a sunny day.

6. HAUMEA HAS ONE OF THE SHORTEST DAYS IN THE ENTIRE SOLAR SYSTEM.

If you lived to be a year old on Haumea, you would be 284 years old back on Earth. And if you think a Haumean year is unusual, that's nothing next to the length of a Haumean day. It takes 3.9 hours for Haumea to make a full rotation, which means it has by far the fastest spin, and thus shortest day, of any object in the solar system larger than 62 miles.

7. HAUMEA'S HIGH SPEED SQUISHES IT INTO A SHAPE LIKE A RUGBY BALL.

haumea rotation gif
Stephanie Hoover, Wikipedia // Public Domain

As a result of this tornadic rotation, Haumea has an odd shape; its speed compresses it so much that rather than taking a spherical, soccer ball shape, it is flattened and elongated into looking something like a rugby ball.

8. HIGH-SPEED COLLISIONS MAY EXPLAIN HAUMEA'S TWO MOONS.

Ortiz says there are several mechanisms that can have led to rings around the dwarf planet: "One of our favorite scenarios has to do with collisions on Haumea, which can release material from the surface and send it to orbit." Part of the material that remains closer to Haumea can form a ring, and material further away can help form moons. "Because Haumea spins so quickly," Ortiz adds, "it is also possible that material is shed from the surface due to the centrifugal force, or maybe small collisions can trigger ejections of mass. This can also give rise to a ring and moons."

9. ONE MOON HAS WATER ICE—JUST LIKE HAUMEA.

Ortiz says that while the rings haven't transformed scientists' understanding of Haumea, they have clarified the orbit of its largest moon, Hi'iaka—it is equatorial, meaning it circles around Haumea's equator. Hi'iaka is notable for the crystalline water ice on its surface, similar to that on its parent body.

10. TRYING TO SEE HAUMEA FROM EARTH IS LIKE TRYING TO LOOK AT A COIN MORE THAN 100 MILES AWAY.

It's not easy to study Haumea. The dwarf planet, and other objects at that distance from the Sun, are indiscernible to all but the largest telescopes. One technique used by astronomers to study such objects is called "stellar occultation," in which the object is observed as it crosses in front of a star, causing the star to temporarily dim. (This is how exoplanets—those planets orbiting other stars—are also often located and studied.) This technique doesn't always work for objects beyond the orbit of Neptune, however; astronomers must know the objects' orbits and the position of the would-be eclipsed stars to astounding levels of accuracy, which is not always the case. Moreover, Ortiz says, their sizes are oftentimes very small, "comparable to the size of a small coin viewed at a distance of a couple hundred kilometers."

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