2015 TB145: Halloween Asteroid Is A Treat For Scientists

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Asteroid 2015 TB145 will make its closest approach to Earth at 1.3 lunar distances around noon (EST) on Saturday. Graphic courtesy of NASA.

Like an interplanetary witch, an object will whizz within a galactic stone’s throw of earth on Saturday.

Since a similar object smashed into the earth 65 million years ago and caused the extinction of half the species on the planet, including the dinosaurs, it may seem like a cosmic trick.

But a collision between the earth and an object this size is not very common.

Still, it makes you think. What if?

Who Found TB145, And How And When Did They Find It?

Despite NASA’s near-Earth observation program, designed to detect large objects that could get dangerously close to the earth, TB145 was not discovered until October 10 by the University of Hawaii’s Panoramic Telescope and Rapid Response System (Pan-STARRS-1). Pan-STARRS-1 continuously scans the sky for anything that moves relative to the background of ‘fixed stars.’

What Took So Long For Astronomers To Find TB145?

Most of the material in the solar system, including witches, goblins, and asteroids, lie within a few degrees of the ecliptic (The ecliptic is the plane defined by the earth’s path around the sun.). Most observations are concentrated in this plane.

Asteroids are pieces of rock, possibly the remnants of a failed or broken planet, that normally orbit the sun between Mars and Jupiter. Astronomers believe that occasionally an asteroid interacts gravitationally with Jupiter in such a way that it can be thrown into a strange orbit or even ejected from the solar system. In addition, comets, visitors from the farthest reaches of the solar system, can have unusual orbits. The orbit of TB145 has been calculated for about 100 years; it passes the earth every three years at an angle of 39 degrees to the ecliptic.

What Happened To The Dinosaurs?

A large object, undoubtedly either an asteroid or comet, struck the earth 65,000,000 years ago and left a crater at the tip of Yucatan, Mexico. The immediate result was fire and brimstone — a rain of molten rock which killed a lot of animals. But the real cataclysm occurred over many years: Dust from the collision obscured the sun and lowered the temperature of the atmosphere. An extended period of reduced sunlight due to dust was probably the main driver of the extinction, disrupting the growth of vegetation at the bottom of the food chain.

Finally, when the dust settled, the earth warmed rapidly because a large amount of carbon dioxide was released by the explosion, increasing the greenhouse effect. The end result was a massive extinction, the likes of which has only been seen five times on Earth. (Some scientists believe we are now in the middle of a sixth extinction — this one anthropogenic.)

TB145 Will Be A Treat For Astronomers

Will TB145 look like the asteroid Eros? Or more like a witch’s broomstick? Photo courtesy of NASA.

It isn’t often that you get to see something no one’s seen before (yes, we all know the riddle about the walnut).

At its closest approach, TB145 will yield views of its surface that are twice as detailed as any observations ever made of an asteroid.

Scientists are most interested in observing the orientation and position of the rocks that make up the asteroid. When an object is large enough (the size of a planet or large moon),  its gravity forces it into a round shape as everything gets smished (smished is a Decoded-coined scientific word that means mashed together into a gravitationally-stable spheroid).

But asteroids are too small, with only a couple of exceptions, to be smished. The rocks that comprise TB145 will just be a jumble of junk; virtually any shape is possible.

There is also a small chance that TB145 is not an asteroid. Plenty of junk was left over after the formation of the sun, planets, and moons. It may turn out that this is a burned-out comet. Or it could be a hybrid asteroid-comet of a type never before seen.

This is the forecast for Saturday morning. The best viewing conditions will be under the high pressure systems (H). Forecast courtesy of NOAA

Can You See TB145 With The Naked Eye?

You will need magnification to view this asteroid. Since its closest approach is in the middle of the day (1 pm, EDT), observations are most likely to succeed in the early morning hours Saturday. Point your telescope towards the constellation Taurus and check the latest estimates of exactly where to look.

Unfortunately TB145 will be traveling at 78,000 miles per hour as it passes us, so at four in the morning it will be considerably farther away than at closest approach.

If we make a triangle of earth, the point of closest approach, and the object’s location at 4 am (EDT) and apply the Pythagorean Theorem, we get D^2 (the distance from Earth to TB145 at 4 am, squared) = 300,000^2 (the distance from the earth to the asteroid at closest approach, squared) + 702,000^2 (the distance from the asteroid at closest approach to the asteroid at 4 am, squared).

Solving, we get approximately D = 760,000 miles. Needless to say, if the closest approach were at night, the object would be much easier to see.

Could It Happen To Us?

The object that hit the earth 65 million years ago was about six miles in diameter TB145 is very much smaller — around a third of a mile in diameter. Approximately 13,000 objects this size or bigger have been identified. If an object this size hit earth, it would inflict catastrophic damage to the area hit and possibly disrupt the weather worldwide for years. But civilization would survive.

Scientists estimate that about 95% of all asteroids the size of the one that caused the dinosaurs’ demise have been discovered and none is a threat to Earth.

The likelihood of a large asteroid or comet colliding with the earth any time soon isn’t great enough to lose sleep over, even on a spooky night like Halloween, but someday ….

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