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7. Closest Approach of a Large Asteroid Before 2027
John Austin

The passage of asteroid 2004 BL86 across the plane of the Earth’s orbit. The asteroid will come into visibility in the northern hemisphere on 26 January 2015. Image courtesy of NASA/JPL-Caltech.

In what promises to be a bumper year for the observation of asteroids and dwarf planets, the asteroid 2004 BL86 is due for a near miss of Earth on 26 January 2015.

The Asteroid Belt

Asteroids and comets come from a belt of objects in orbit around the sun between the orbits of Mars and Jupiter. Occasionally, the gravity of Jupiter perturbs, and diverts these objects to the inner solar system, where they occasionally approach Earth.

As part of its Near Earth Observation program, NASA is keeping track of objects which are expected at some point to pass close to the Earth, so that we can be aware of any impending danger. 2004 BL86 does not pose any danger, but it is worth observing as the next near miss by an asteroid of a similar size is not due for another 12 years.

Asteroid 2004 BL86: Near Miss

The asteroid 2004 BL86, which has a diameter between 400 and 900 m, will come within about 1.2 million km of Earth on 26 January. This will give Earth-based astronomers a unique opportunity to observe it.

During the near miss, this asteroid should reach magnitude 9 or 10. You won’t be able to see it with the naked eye, but will be able to observe its motion through the constellations using powerful binoculars or a small telescope.

This object has an orbital period of about 1.84 years but because of the high eccentricity of its orbit, it will not be expected near Earth again for about 200 years. For the last week it has been visible in the Southern Hemisphere, but is now visible in the Northern Hemisphere (see chart).

Comparison With the 2013 Asteroid Duende

It is tempting to compare this year’s asteroid with the near miss of asteroid 367943 Duende, which passed within 28,000 km of the Earth’s surface on 15 February 2013. Sixteen hours earlier, a meteor caused a spectacular display over Chelyabinsk, Russia, including sonic booms and damage to windows. Car video cameras recorded the event in Chelyabinsk, and you can find these videos on Youtube.

However, although you might expect that the Earth’s gravity could partially shatter a small asteroid, the Chelyabinsk meteor and the asteroid Duende were unrelated. Therefore, we can expect the 2004 BL86 asteroid to pass by without any special fireworks.

Asteroids and Dwarf Planets

Asteroids, comets and dwarf planets are left-over material from the formation of the planets in the solar system. One of the main differences in appearance between asteroids and dwarf planets is that the higher gravity (due to their higher mass) of dwarf planets have, over time, tended to reform them into a more spherical shape. Asteroids, by comparison, often have very irregular shapes.

We are all familiar with Pluto, of course, which is the largest of the dwarf planets. Pluto was downgraded from full planet status in 2006 for a variety of reasons. Other objects include Ceres, which has a diameter of about 950 km, and makes up about 30% of the total mass of the asteroid belt.

The mass of Ceres is about 7.2% of that of Pluto. The next largest object in the asteroid belt is Vesta, with a diameter of about 525 km and a mass of 2% of that of Pluto.

Last year, observations by the Dawn spacecraft provided outstanding data and images of Vesta. Dawn is now approaching Ceres, and it will go into orbit around it in early March.

Processed image of the dwarf planet Ceres taken on January 13, 2015, from the Dawn spacecraft Image courtesy of NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

At the moment, the images are of similar quality to those that can be viewed from the Hubble Space Telescope, but Ceres still only appears like a fuzzy blob.

Future Observations of Ceres and Pluto

Although Dawn is no longer operating at 100% capability, when it reaches Ceres, we should still have far better images and data on the dwarf planet than we’ve ever had before.

Finally, Pluto itself is due for a fly by in July this year. At the moment, some structure is visible in the images. Images from the Hubble space telescope are of comparable quality, but the New Horizons spacecraft will steadily acquire better images as the nearest approach takes place.

Resources

  • NASA. Asteroid to Fly By Earth Safely on January 26. (2014). Accessed on January 26, 2015
  • NASA. Dawn. (2015). Accessed on January 26, 2015
  • NASA. Near Earth Object Program. (2015). Accessed on January 26, 2015

Article initially prepared 26 January 2015 for decodedscience.com and transferred to enigmascientific.com on 28 January 2015.

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Website revised by John Austin, 28/1/2015. © Enigma Scientific Publishing, 2015.