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'Halloween asteroid' 2015 TB145 safely zips past the Earth-Moon system on Oct 31, 2015
OUT OF THIS WORLD | What's Up In Space

A 'scary' Halloween pass by Asteroid 2015 TB145? Not really

Scott Sutherland
Meteorologist/Science Writer

Wednesday, October 28, 2015, 5:00 PM - Although it's on Halloween, should we be frightened by 2015 TB145's Saturday flyby? Plus, a new study finds a link between asteroid showers and mass extinctions, and Kepler spies a real "Death Star" ripping apart a planet. It's What's Up In Space!

A "scary" Halloween flyby?

On October 31, 2015, at just after 1 p.m. EDT, a large asteroid will buzz past Earth and the Moon, travelling at a relative speed of about 126,000 kilometres per hour - "unusually" fast, according to NASA.

This asteroid, now known as 2015 TB145, but nicknamed "Spooky" by some, was first spotted on October 10, 2015 by the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS), located on Hawaii's Mount Haleakala. "Spooky" is estimated at being between 200-600 metres wide, and since its discovery, the track of the asteroid shows that it will be making a rather close pass by Earth - at least relative to the size of the solar system.

At the time of closest approach, 2015 TB145 will come to within about 487,000 kilometres of our planet, or a little over 100,000 kilometres farther than the the Moon. About two and a half hours before, it will pass even closer to the Moon, at a distance of about 286,000 km.

Trajectory of 2015 TB145 as it passes Earth and the Moon on October 31, 2015. Credit: Celestia, with labels by author.

Should we be frightened by this? Concerned? Vaguely anxious?


Asteroid 2015 TB145 is certainly a Near-Earth Object, and it is one of the most recent additions to NASA's list of Potentially Hazardous Asteroids (those of a certain brightness/size that come within 7.5 million km of Earth). However, as it is flying by at a distance farther away than the Moon, this is a harmless pass.

Great scientific opportunity

Far from scary, the passing of 2015 TB145 will be an excellent opportunity for the scientific community.

During this flyby NASA will be aiming its Goldstone radio antennas at the asteroid, to obtain detailed radar images of this unusually fast, possibly cometary object. The Goldstone astronomers have labeled 2015 TB145 as "one of the best radar targets of the year" for their observations, and they anticipate getting images back with a resolution of about 2 metres per pixel. This will not only confirm the size of the asteroid, but also its shape, and potentially its composition.

"The flyby presents a truly outstanding scientific opportunity to study the physical properties of this object," they wrote in their planning notes.

Update (Oct 28, 2015 @ 5:00 p.m. EDT) - As some reports about this asteroid have raised concerns about impacts with either Earth or the Moon, here are some notes about the object to explain certain aspects of its orbit and nature:
1) NASA currently lists this object with a "condition code" of 6. This is on a scale of 0-9, with 0 being a well-defined orbit and 9 being a high uncertain orbit. Being closer to the "uncertain" end of the scale, there are still errors in the plot of 2015 TB145's orbit, however this only has an appreciable effect in the long-term future - years or decades from now. With only a few days until flyby, the object's orbit is known well enough that no impact is even hinted at.
2) Scientists watching the object are curious about its unusual orbit, because it looks more like the orbit of a comet than an asteroid. However, that does not mean that 2015 TB145 is a comet. This close to the Sun, a comet would be producing a bright coma and tails, but that is not observed with this object. At most, it could be an "extinct comet" - a comet that has lost most or all of its ice and volatile gases, and now behaves as an asteroid.
3) Why haven't we seen this asteroid before, given how big it is? Mostly bad timing and bad luck. 2015 TB145 appears to have an orbital period of 3 years, 25 days and 13 hours (+/- 5 days or so). While it may seem that it should come around and be visible to us every 3 years, that extra time - 25 days and 13 hours (+/- 5 days) - really matters. It's never in the same place in the Earth's sky each time it comes around to cross our orbit, and often it's lost in the glare of the daylit or dawn/dusk sky. Also, due to the shape of its orbit, only a telescope in the far reaches of the southern hemisphere could hope to catch it in the deepest, darkest part of the night sky, but even then, it is usually much farther away at that time, making it more difficult to spot.

This year appears to be the first time in nearly 100 years and the last time until at least the year 2200 that 2015 TB145 comes close enough to Earth and is in the right part of the sky to be spotted.

Mass extinctions linked to showers of asteroids and comets

Asteroid 2015 TB145 may be safely passing by our world, but we have ample evidence to show that we have been hit in the past, and by some fairly sizable objects.

Now, a new study is showing a link - a 26 million year pattern - between major extinction events here on Earth, and the frequency of major asteroid and comet impacts in the past.

Graph of major cratering events on Earth over time, with arrows indicating dates of mass extinctions. Credit: Michael Rampino/New York University

The size of the mass extinction doesn't correlate very well with the crater formation rate in the above graph. For example, the rate of cratering 38 million years ago is one of the highest rates shown in the past 260 million years, however the Eocene–Oligocene extinction event that took place at that time was minor compared to the K-T extinction event 66 million years ago, when a 10 km wide asteroid slammed into what is now the Gulf of Mexico, killing off around 75 per cent of all species alive on the planet at the time.

According to the research, penned by New York University professor Michael Rampino and Ken Kaldiera, of the Carnegie Institution for Science, making a specific claim between these kinds of events is controversial. Still, this roughly 26 million year connection between impacts and extinctions could hint at some kind of link.

"The correlation between the formation of these impacts and extinction events over the past 260 million years is striking and suggests a cause-and-effect relationship," Rampino said in a statement.

Interesting. Scary? Maybe in another 8 million years or so.

Kepler spies a "zombie" star tearing apart a planet

In this artist's conception, a Ceres-like asteroid is slowly disintegrating as it orbits a white dwarf star. Credit: Mark A. Garlick / markgarlick.com

As it now orbits around the Sun on its "K2" mission, the Kepler space telescope continues its search for planets around other stars by watching for transits, a characteristic dip in brightness that occurs when a planet orbiting there passes between us and the star.

Around 570 light years away, in the constellation Virgo, there's a tiny white dwarf star - the "dead" remnant that a star like our Sun leaves behind when it reaches the end of its stellar life span. These white dwarfs still shine brightly, though, continuing in a "zombie" state and still interacting with the objects around it.

Until now, astronomers had never witnessed a planet transiting across a white dwarf, but that's exactly what they've discovered around this particular stellar remnant - a small planet, roughly the size of the dwarf planet Ceres, that orbits around the dwarf star every 4.5 hours.

Remarkably, that puts the planet's distance from the white dwarf at only about twice the distance between the Earth and the Moon.

Even more amazing is that this planet represents the very first evidence of a white dwarf star tearing apart a planet that orbits it. Why is that important?

According to the Harvard-Smithsonian Center for Astrophysics:

When a Sun-like star reaches the end of its life, it swells into a red giant and sloughs off its outer layers. The hot, Earth-sized core that remains is a white dwarf star, and generally consists of carbon and oxygen with a thin hydrogen or helium shell.
Sometimes, though, astronomers find a white dwarf that shows signs of heavier elements like silicon and iron in its light spectrum. This is a mystery because a white dwarf's strong gravity should quickly submerge these metals.
"It's like panning for gold - the heavy stuff sinks to the bottom. These metals should sink into the white dwarf's interior where we can't see them," explains Harvard co-author John Johnson (CfA).
Theorists speculated that white dwarfs showing evidence of heavy metals became "polluted" when they consumed rocky planets or asteroids. However, the evidence was often circumstantial. A fraction of polluted white dwarfs showed signs of surrounding debris disks, but the origin of the disks was uncertain. This system shows all three: a polluted white dwarf, a surrounding debris disk, and at least one compact, rocky object.

Therefore, this represents the very first hard evidence of how these white dwarfs become "polluted" with these other elements.

Over a thousand confirmed exoplanets and thousands more awaiting confirmation, and now two new firsts from the same "zombie" star system. The Kepler mission is truly remarkable.

Sources: NASA/JPL-Caltech | NASA Goldstone | Royal Astronomical Society | Harvard-Smithsonian Center for Astrophysics

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