Hygiea, Vesta, and Ceres


New ground-based observations with ESO’s SPHERE instrument on the Very Large Telescope have revealed that the surface of the asteroid Hygiea lacks a large impact crater. Because it was formed from one of the largest impacts in the history of the asteroid belt, astronomers were expecting to find at least one large, deep impact basin, similar to the one on Vesta (bottom right in the central panel).

The new study also found that Hygiea is spherical. That would mean that it rather than Ceres is the smallest dwarf planet in the Solar System. Hygiea’s diameter is just over 430 km, a bit less than half that of Ceres (950 km).

Image Credit: ESO

A Near Earth Asteroid


NearEarthAsteroidThe greenish-yellow dot in the upper left is the potentially hazardous near-Earth object 1998 KN3 moving past a cloud of dense gas and dust near the Orion nebula in the far, far background. NEOWISE, the asteroid-hunting portion of the Wide-field Infrared Survey Explorer, or WISE, mission, took this infrared picture. Because near-Earth asteroids are warmed by the Sun to roughly room temperature, they glow brightly at the infrared.

Infrared light from asteroids is used to measure their sizes. Combined with visible-light observations, that data can also measure the reflectivity of their surfaces. The WISE data reveal that this asteroid is about 1.1 km in diameter and reflects only about 7 percent of the visible light that falls on its surface. It is relatively dark.

In this image blue denotes shorter infrared wavelengths and red, longer. Hotter objects emit shorter-wavelength light; they appear blue. Stars with temperatures of thousands of degrees are blue. The coldest gas and dust are red. The asteroid appears greenish-yellow in the image because it is about room temperature—cooler than the stars, but warmer than the dust.

Image Credit: NASA

Asteroids!


This animation shows the first four year’s progress of NASA’s Near-Earth Object Wide-field Survey Explorer (NEOWISE) mission following the repurposing of the WISE satellite in December, 2013. Green dots represent near-Earth objects. Gray dots represent all other asteroids which are mainly in the main asteroid belt between Mars and Jupiter. Yellow squares represent comets.

Image Credit: NASA

Asteroids!


These detailed images were taken by ESO’s Very Large Telescope at the Paranal Observatory in Chile. Clockwise from top left, the asteroids shown here are 29 Amphitrite, 324 Bamberga, 2 Pallas, and 89 Julia.

2 Pallas was named after the Greek goddess Pallas Athena and is about 510 km wide. It’s the third largest asteroid in the main belt and one of the biggest asteroids in the entire Solar System. It contains about 7% of the mass of the entire asteroid belt andt was once classified as a planet.

89 Julia is about one-third the size of Pallas. It’s classified as a stony or S-type asteroid, as is 29 Amphitrite. 324 Bamberga, one of the largest carbonaceous or C-type asteroids in the asteroid belt. C-type asteroids may actually be bodies from the outer Solar System which followed the migration of the giant planets inward.

In total, the asteroid belt contains just 4% of the mass of the Moon, with about half of this mass contained in the four largest: the dwarf planet Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea.

Image Credit: ESO

Asteroid Photobombing


This Hubble image of a random patch of sky is part of a survey called Frontier Fields and was assembled from multiple exposures. It contains thousands of distant galaxies and the trails of asteroids moving through the field of view. The asteroid trails appear as curved or streaks. The combined image show 20 sighting of 7 different asteroids.

Image Credit: NASA / ESA / STScI

Radar Astronomy and Asteroids


2017bq6Astronomers use large radio telescopes as radar sets to look at nearby objects in space. These images of asteroid 2017 BQ6 are from data collected using the Goldstone Solar System Radar in the Mojave Desert. The images were taken on 7 February as the asteroid flew by about 2.5 million km from Earth. The asteroid is about 200 m across and has an unusually squared off shape.

Image Credit: NASA

VLT Sees NEO


VLT Sees NEONEOs are asteroids or comets that come very close to the Earth’s orbit. More than 600,000 asteroids are known in the Solar System, and more than 10,000 of them are NEOs. Their sizes range from metres to tens of kilometres. Some NEOs could hit our planet and, depending on their size, produce considerable damage. While the chance of a large object hitting the Earth is very small, it could produce a great deal of destruction and loss of life—as the dinosaurs discovered 50 million or so years ago.

Up to now the asteroid 2009 FD had been ranked among the top five objects in a list of the most dangerous objects, but new observations with ESO’s Very Large Telescope (VLT) have now shown that it is far less likely to hit the Earth than had been feared. The calculations show there is still a small chance of an impact between the years 2185 and 2198.

Image Credit: ESO

A Near Earth Asteroid


NearEarthAsteroidThe greenish-yellow dot in the upper left is the potentially hazardous near-Earth object 1998 KN3 moving past a cloud of dense gas and dust near the Orion nebula in the far, far background. NEOWISE, the asteroid-hunting portion of the Wide-field Infrared Survey Explorer, or WISE, mission, took this infrared picture. Because near-Earth asteroids are warmed by the Sun to roughly room temperature, they glow brightly at the infrared.

Infrared light from asteroids is used to measure their sizes. Combined with visible-light observations, that data can also measure the reflectivity of their surfaces. The WISE data reveal that this asteroid is about 1.1 km in diameter and reflects only about 7 percent of the visible light that falls on its surface. It is relatively dark.

In this image blue denotes shorter infrared wavelengths and red, longer. Hotter objects emit shorter-wavelength light; they appear blue. Stars with temperatures of thousands of degrees are blue. The coldest gas and dust are red. The asteroid appears greenish-yellow in the image because it is about room temperature—cooler than the stars, but warmer than the dust.

Image Credit: NASA

Potentially Hazardous Asteroids


hazardous_asteroidsSome asteroids are dangerous, but the chance of an asteroid hitting the Earth during any given year is low. But some past mass extinction events have been linked to asteroid impacts, so some astronomers are cataloging those asteroids that might be a danger to Earth. Here are the orbits of the over 1,000 known Potentially Hazardous Asteroids. These chunks of rock and ice are all over 140 meters across and can come within 7.5 million kilometers of Earth (about 20 times the distance to the Moon). None of these should strike the Earth during the next century, but not every PHA has been found.Furthermore, many of the orbits become hard to predict over periods longer than 100 years. If an asteroid of this size were to strike in an ocean (the Earth’s surface is 70% ocean), it could raise dangerous tsunamis. Bits of rocks and ice strike the Earth every day, but few are large enough to make it through the atmosphere without being vaporized.

Image Credit: NASA

Another NEO


neo20130624-fullMeet asteroid 2013 MZ5 as seen by the University of Hawaii’s PanSTARR-1 telescope. In this animated gif, the asteroid moves diagonally relative to a fixed background of stars. Near-Earth objects (NEOs) are asteroids and comets that can approach within about 45 million km of the Earth’s orbit. Those detected to date range in size from as small as a few meters to as large 40 km for the largest near-Earth asteroid 1036 Ganymed. Asteroid 2013 MZ5 is the 10,000th NEO detected. It’s estimated to be about 300 m across.

Image credit: PS-1/UH

Friday’s Asteroid


First of all, asteroids aren’t caused by global warming. They’re the floor sweepings left over from the formation of the planets billions of years ago. Some of them are pretty big. Indeed, one of them, Ceres, is large enough to qualify as a dwarf planet. Most of them are tiny.

Several tons worth of the tiny asteroids collide with the Earth each day. Almost all of them burn up in the atmosphere as meteors. A few make it to the ground as meteorites. Every thousand years or so, a large meteor weighing tens of tons smacks into the ground releasing energy equivalent to a nuclear weapon. This happened in Siberia in 1908. Larger, Earth-shattering kabooms occur every few million years when an asteroid several hundred metres (or larger) in diameter hits. A large strike about 66 million years ago ended the Age of Dinosaurs.

This Friday’s asteroid will miss us. If it were to hit, the energy release would be roughly equivalent to a 2 megaton nuke, inconvenient for the local neighborhood but hardly Earth-shattering.

We frequently discover new asteroids. One was discovered in 1998 as the long blue streak in this archival image taken by the Hubble Space Telescope.asteroidstreak_hst_960