Dawn Creates Guide To Vesta’s Hidden Attractions

The first colorful composite image shows the flow of material inside and outside a crater called Aelia on the giant asteroid Vesta. The area is around 14 degrees south latitude. To the naked eye, these structures would not be seen. But here, they stand out in blue and red. The images that went into this composite were obtained by NASA’s Dawn space probe.

The second colorful image shows material northwest of the crater Sextilia on the giant asteroid Vesta. Sextilia, located around 30 degrees south latitude, is at the bottom right of this image.

In this image, the entire color spectrum of Vesta becomes visible. While a large asteroid impact probably brought the black material, the red material may have been melted by the impact.

The composite image was created by assigning ratios of color information collected from several color filters in visible light and near-infrared light to maximize subtle differences in lithology (the physical characteristics of rock units, such as color, texture and composition). The color scheme pays special attention to the iron-rich mineral pyroxene.

Image Credit: NASA/JPL-Caltech/UCLAMPS/DLR/IDA
Hubble views extraordinary multi-tailed asteroid P/2013 P5

These NASA/ESA Hubble Space Telescope images reveal a never-before seen set of six comet-like tails radiating from a body in the asteroid belt and designated P/2013 P5.
The asteroid was discovered as an unusually fuzzy looking object by astronomers using the Pan-STARRS survey telescope in Hawaii. The multiple tails were discovered in Hubble images taken on 10 September 2013. When Hubble returned to the asteroid on 23 September its appearance had totally changed — it looked as if the entire structure had swung around.
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Credit: NASA, ESA, D. Jewitt (University of California, Los Angeles), J. Agarwal (Max Planck Institute for Solar System Research), H. Weaver (Johns Hopkins University Applied Physics Laboratory), M. Mutchler (STScI), and S. Larson (University of Arizona)

Hubble views extraordinary multi-tailed asteroid P/2013 P5

These NASA/ESA Hubble Space Telescope images reveal a never-before seen set of six comet-like tails radiating from a body in the asteroid belt and designated P/2013 P5.

The asteroid was discovered as an unusually fuzzy looking object by astronomers using the Pan-STARRS survey telescope in Hawaii. The multiple tails were discovered in Hubble images taken on 10 September 2013. When Hubble returned to the asteroid on 23 September its appearance had totally changed — it looked as if the entire structure had swung around.

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Credit: NASA, ESA, D. Jewitt (University of California, Los Angeles), J. Agarwal (Max Planck Institute for Solar System Research), H. Weaver (Johns Hopkins University Applied Physics Laboratory), M. Mutchler (STScI), and S. Larson (University of Arizona)

Moons Around Asteroid Kleopatra

Asteroid (216) Kleopatra has been interesting to astronomers for a long time because its brightness is highly variable, but it seems to get more interesting every time somebody looks at it with a new instrument. In 2000 it was found to be “dog-bone” shaped; in 2008 it was discovered to have two moons.

Like the ancient Egyptian queen it was named for, the asteroid Kleopatra has birthed twins — a pair of moons that have helped scientists learn that the huge space rock is a rubble pile rather than a chunk of solid rock.

These two moons, named Alexhelios and Cleoselene after the twin children of the queen, were discovered in 2008. Now, astronomers studying their orbits have deduced that their parent asteroid is a jumble of loosely held rocks.

There are a number of smaller asteroids throughout the solar system that are loose, gravitationally bound piles of rock rather than solid objects.

But to find one in such a large system is surprising. At about 135 miles (217 km) in length, Kleopatra is among the largest of these rubble pile asteroids discovered over the past few years, topped only by 174-mile (280 km) 87 Sylvia.

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Credit: UC Berkeley NewsCente/Nola Taylor Redd

Russian Scientists Report Asteroid Near-Miss

A 15-meter (approximately 50 feet) asteroid, similar to the one that exploded above Russia in February, was detected hours before it narrowly missed the Earth over the weekend, Russian scientists said.

Vladimir Lipunov of the Moscow State University and the Sternberg Astronomical Institute said on Sunday a network of telescopes operated by his team recorded a celestial body approaching the planet.

The asteroid was discovered on Friday night by our station near Lake Baikal and nine hours later it flew within 11,300 kilometers of the Earth surface, below the orbit of geostationary satellites. It was about 15 meters in size.

The scientists originally thought that it could be a man-made object, such as a spent rocket booster, but rejected the idea when they couldn’t find a match in the space junk catalogue.

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Credit: Moscow State University/MASTER/Vladimir Lipunov

How to deflect an asteroid

Gareth Collins of Imperial College London’s Department of Earth Science & Engineering explains how to defeat near-Earth objects. Sorry, Bruce Willis.
Find the threat “Near-Earth objects are pieces of rock or ice in the solar system whose orbit occasionally brings them close to Earth,” says Collins. Their small size and distance from Earth make them difficult to see, but telescope arrays have detected 85 per cent of objects more than 1km in diameter. “Thousands reach the Earth every year, but hazards are infrequent. The ten-kilotonne object over Chelyabinsk in February was a once-a-century event.”
Assess the risk The damage that an asteroid impact can cause depends on factors such as its size, speed, density and where it lands. Collins has developed a website (impact.ese.ic.ac.uk) to help estimate threats. “Asteroids about 1.5km in diameter are believed to be large enough to disperse debris worldwide,” he says. “The impact of an object the size of a city block would not cause global damage, but could have far-reaching consequences if it occurred in an ocean off a populous place.”
Deflect it Whether or not a deflection mission is possible depends on the asteroid’s size and how much warning there is. “With more than ten years’ warning, one of a number of strategies could be used to knock it off course,” Collins says. Colliding a spacecraft with the asteroid is the most practical and could be used on asteroids up to a few hundred meters across; adding a nuclear warhead would be better for objects up to 1km across. Or use a spacecraft as a “gravity tractor” to pull the object away from Earth.


Image credit: Tavis Coburn

How to deflect an asteroid

Gareth Collins of Imperial College London’s Department of Earth Science & Engineering explains how to defeat near-Earth objects. Sorry, Bruce Willis.

Find the threat
“Near-Earth objects are pieces of rock or ice in the solar system whose orbit occasionally brings them close to Earth,” says Collins. Their small size and distance from Earth make them difficult to see, but telescope arrays have detected 85 per cent of objects more than 1km in diameter. “Thousands reach the Earth every year, but hazards are infrequent. The ten-kilotonne object over Chelyabinsk in February was a once-a-century event.”

Assess the risk
The damage that an asteroid impact can cause depends on factors such as its size, speed, density and where it lands. Collins has developed a website (impact.ese.ic.ac.uk) to help estimate threats. “Asteroids about 1.5km in diameter are believed to be large enough to disperse debris worldwide,” he says. “The impact of an object the size of a city block would not cause global damage, but could have far-reaching consequences if it occurred in an ocean off a populous place.”

Deflect it
Whether or not a deflection mission is possible depends on the asteroid’s size and how much warning there is. “With more than ten years’ warning, one of a number of strategies could be used to knock it off course,” Collins says. Colliding a spacecraft with the asteroid is the most practical and could be used on asteroids up to a few hundred meters across; adding a nuclear warhead would be better for objects up to 1km across. Or use a spacecraft as a “gravity tractor” to pull the object away from Earth.

Image credit: Tavis Coburn

Meteorite minerals hint at earth extinctions, climate change

Scientists think that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. Data from NASA’s WISE mission likely rules out the leading suspect, a member of a family of asteroids called Baptistina, so the search for the origins of the dinosaur-killing asteroid goes on.
A huge asteroid that wiped out the dinosaurs may not have been the only cosmic event to cause mass extinctions or change Earth’s climate. Tiny minerals leftover from many smaller meteorites could provide the geological evidence needed to show how rocks falling from the sky changed the course of life’s evolution on our planet more than just once.
The tiny minerals called spinels—about the size of a sand grain—can survive the harshest weather and chemical changes on Earth’s surface. Swedish researchers hope to collect enough of the spinels in different parts of the world to connect the dots between the breakup of huge asteroids in space and certain extinction or climate events during Earth’s history.
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Credit: NASA/JPL-Caltech/Lund University

Meteorite minerals hint at earth extinctions, climate change

Scientists think that a giant asteroid, which broke up long ago in the main asteroid belt between Mars and Jupiter, eventually made its way to Earth and led to the extinction of the dinosaurs. Data from NASA’s WISE mission likely rules out the leading suspect, a member of a family of asteroids called Baptistina, so the search for the origins of the dinosaur-killing asteroid goes on.

A huge asteroid that wiped out the dinosaurs may not have been the only cosmic event to cause mass extinctions or change Earth’s climate. Tiny minerals leftover from many smaller meteorites could provide the geological evidence needed to show how rocks falling from the sky changed the course of life’s evolution on our planet more than just once.

The tiny minerals called spinels—about the size of a sand grain—can survive the harshest weather and on Earth’s surface. Swedish researchers hope to collect enough of the spinels in different parts of the world to connect the dots between the breakup of huge asteroids in space and certain extinction or during Earth’s history.

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Credit: NASA/JPL-Caltech/Lund University

Searching for the Little Prince’’s homeland 

Asteroids are small solid objects circling around the Sun, following orbits located mainly in the so-called “asteroid belt”, an ill-defined region between Mars and Jupiter. Antoine de Saint-Exupéry’s most famous character, the Little Prince, lived on a volcanic asteroid whose volcanoes the Prince took care of.
But it is believed that real asteroids are seldom volcanic. A volcanic or, more properly, basaltic asteroid, forms only if the body has melted partially during its history, allowing heavy elements (metals) to sink towards its centre, leaving lighter rocks on the mantle, and forming a volcanic crust of basalt through emission of lava flows. This process is called differentiation, and an asteroid has to be quite large for it to happen.
Only one big asteroid shows a basaltic crust, Vesta, and there is a complete family of smaller objects showing similar surface and orbital characteristics, thought to be fragments taken away from Vesta by large impacts: these asteroids constitute the “Vesta family.” However, there are reasons to expect that these objects should not be so scarce. Astronomers think that there should have existed many clones of Vesta in the old Solar System, and some of them or, at least, some of their fragments, could still be out there. 
Recent studies have discovered that several tiny near-Earth asteroids are basaltic and they are not necessarily lost members of the Vesta family. Furthermore, a basaltic asteroid, Magnya, was found in the outer part of the asteroid belt in 2000. 
The Little Prince lived on asteroid B612, bearing three volcanoes and one rose. Real volcanic asteroids are already here. But, where are the roses? 
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Credit: Calar Alto Observatory

Searching for the Little Prince’’s homeland

Asteroids are small solid objects circling around the Sun, following orbits located mainly in the so-called “asteroid belt”, an ill-defined region between Mars and Jupiter. Antoine de Saint-Exupéry’s most famous character, the Little Prince, lived on a volcanic asteroid whose volcanoes the Prince took care of.

But it is believed that real asteroids are seldom volcanic. A volcanic or, more properly, basaltic asteroid, forms only if the body has melted partially during its history, allowing heavy elements (metals) to sink towards its centre, leaving lighter rocks on the mantle, and forming a volcanic crust of basalt through emission of lava flows. This process is called differentiation, and an asteroid has to be quite large for it to happen.

Only one big asteroid shows a basaltic crust, Vesta, and there is a complete family of smaller objects showing similar surface and orbital characteristics, thought to be fragments taken away from Vesta by large impacts: these asteroids constitute the “Vesta family.” However, there are reasons to expect that these objects should not be so scarce. Astronomers think that there should have existed many clones of Vesta in the old Solar System, and some of them or, at least, some of their fragments, could still be out there.

Recent studies have discovered that several tiny near-Earth asteroids are basaltic and they are not necessarily lost members of the Vesta family. Furthermore, a basaltic asteroid, Magnya, was found in the outer part of the asteroid belt in 2000.

The Little Prince lived on asteroid B612, bearing three volcanoes and one rose. Real volcanic asteroids are already here. But, where are the roses?

Full Article

Credit: Calar Alto Observatory

Asteroid Zips By Orion

This image shows the potentially hazardous near-Earth object 1998 KN3 as it zips past a cloud of dense gas and dust near the Orion nebula. NEOWISE, the asteroid-hunting portion of the Wide-field Infrared Survey Explorer, or WISE, mission, snapped infrared pictures of the asteroid, seen as the yellow-green dot at upper left. Because asteroids are warmed by the sun to roughly room temperature, they glow brightly at the infrared wavelengths used by WISE.
Astronomers use infrared light from asteroids to measure their sizes, and when combined with visible-light observations, they can also measure the reflectivity of their surfaces. The WISE infrared data reveal that this asteroid is about .7 mile (1.1 kilometers) in diameter and reflects only about 7 percent of the visible light that falls on its surface, which means it is relatively dark.
In this image, blue denotes shorter infrared wavelengths, and red, longer. Hotter objects emit shorter-wavelength light, so they appear blue. The blue stars, for example, have temperatures of thousands of degrees. The coolest gas and dust appears red. The asteroid appears yellow in the image because it is about room temperature: cooler than the distant stars, but warmer than the dust.


Credit:  NASA/JPL-Caltech

Asteroid Zips By Orion

This image shows the potentially hazardous near-Earth object 1998 KN3 as it zips past a cloud of dense gas and dust near the Orion nebula. NEOWISE, the asteroid-hunting portion of the Wide-field Infrared Survey Explorer, or WISE, mission, snapped infrared pictures of the asteroid, seen as the yellow-green dot at upper left. Because asteroids are warmed by the sun to roughly room temperature, they glow brightly at the infrared wavelengths used by WISE.

Astronomers use infrared light from asteroids to measure their sizes, and when combined with visible-light observations, they can also measure the reflectivity of their surfaces. The WISE infrared data reveal that this asteroid is about .7 mile (1.1 kilometers) in diameter and reflects only about 7 percent of the visible light that falls on its surface, which means it is relatively dark.

In this image, blue denotes shorter infrared wavelengths, and red, longer. Hotter objects emit shorter-wavelength light, so they appear blue. The blue stars, for example, have temperatures of thousands of degrees. The coolest gas and dust appears red. The asteroid appears yellow in the image because it is about room temperature: cooler than the distant stars, but warmer than the dust.

Credit: NASA/JPL-Caltech

NASA Spacecraft Reactivated to Hunt for Asteroids

This artist’s concept shows the Wide-field Infrared Survey Explorer, or WISE spacecraft, in its orbit around Earth. In September of 2013, engineers will attempt to bring the mission out of hibernation to hunt for more asteroids and comets in a project called NEOWISE.
From 2010 to 2011, the WISE mission scanned the sky twice in infrared light not just for asteroids and comets but also stars, galaxies and other objects. Back then, the asteroid-hunting portion of the mission was named NEOWISE, which combines the acronyms for near-Earth objects (NEOs) and WISE. NEOs are those asteroids with orbits that come relatively close to Earth. Now, in its second “lease on life,” the mission will be dedicated to asteroid and comet surveying.
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Credit: NASA/JPL-Caltech

NASA Spacecraft Reactivated to Hunt for Asteroids

This artist’s concept shows the Wide-field Infrared Survey Explorer, or WISE spacecraft, in its orbit around Earth. In September of 2013, engineers will attempt to bring the mission out of hibernation to hunt for more asteroids and comets in a project called NEOWISE.

From 2010 to 2011, the WISE mission scanned the sky twice in infrared light not just for asteroids and comets but also stars, galaxies and other objects. Back then, the asteroid-hunting portion of the mission was named NEOWISE, which combines the acronyms for near-Earth objects (NEOs) and WISE. NEOs are those asteroids with orbits that come relatively close to Earth. Now, in its second “lease on life,” the mission will be dedicated to asteroid and comet surveying.

Full Article

Credit: NASA/JPL-Caltech

All Of The Asteroids That Could Potentially End The World

Here’s the path of the nearly 1,400 asteroids that would cause “major devastation” if they hit our planet.
It’s no surprise that NASA is keeping track of all potentially hazardous objects, or PHOs, that surround our planet. If it’s closer than 4.6 million miles away and larger than about 350 feet in diameter, NASA’s watching it. And if a comet or asteroid’s orbit comes close enough to ours that there’s some potential for it to collide with our planet, NASA classifies it as a PHO. If something that size smacked Earth, it’d cause a major tsunami (if it hit water) or major regional destruction (if it hit land).
There are 1,397 known potentially hazardous asteroids (PHAs) at the moment, which you can see in this list. (The other PHOs are comets.) But why look at a list when you can look at a massive gorgeous picture? The image above, taken from NASA/JPL’s Photojournal, shows all 1,397 of those PHAs as represented by their orbits. Kind of amazing that we haven’t been hit by one, isn’t it?


Credit: NASA/Dan Nosowitz

All Of The Asteroids That Could Potentially End The World

Here’s the path of the nearly 1,400 asteroids that would cause “major devastation” if they hit our planet.

It’s no surprise that NASA is keeping track of all potentially hazardous objects, or PHOs, that surround our planet. If it’s closer than 4.6 million miles away and larger than about 350 feet in diameter, NASA’s watching it. And if a comet or asteroid’s orbit comes close enough to ours that there’s some potential for it to collide with our planet, NASA classifies it as a PHO. If something that size smacked Earth, it’d cause a major tsunami (if it hit water) or major regional destruction (if it hit land).

There are 1,397 known potentially hazardous asteroids (PHAs) at the moment, which you can see in this list. (The other PHOs are comets.) But why look at a list when you can look at a massive gorgeous picture? The image above, taken from NASA/JPL’s Photojournal, shows all 1,397 of those PHAs as represented by their orbits. Kind of amazing that we haven’t been hit by one, isn’t it?

Credit: NASA/Dan Nosowitz

Cruithne, Earth’s “second moon”

753 Cruithne is an asteroid in orbit around the Sun in 1:1 orbital resonance with the Earth. It is a minor planet in solar orbit that, relative to Earth, orbits in a bean-shaped orbit that ultimately effectively describes a horseshoe, and which can transition into a quasi-satellite orbit. It has been incorrectly called “Earth’s second moon”. Cruithne does not orbit Earth and at times it is on the other side of the Sun. Its orbit takes it inside the orbit of Mercury and outside the orbit of Mars. Cruithne orbits the Sun in about 1 year but it takes 770 years for the series to complete a horseshoe-shaped movement around the Earth.

Shape of Vesta

These images from NASA’s Dawn mission show the topography of the northern and southern hemispheres of the giant asteroid Vesta, updated with pictures obtained during Dawn’s last look back. Around the time of Dawn’s departure from Vesta in the late summer of 2012, dawn was beginning to creep over the high northern latitudes, which were dark when Dawn arrived in the summer of 2011.

These color-shaded relief maps show the northern and southern hemispheres of Vesta, derived from images analysis. Colors represent distance relative to Vesta’s center, with lows in violet and highs in red. In the northern hemisphere map above (1st image), the surface ranges from lows of minus 13.82 miles (22.24 kilometers) to highs of 27.48 miles (44.22 kilometers). Light reflected off the walls of some shadowed craters at the north pole (in the center of the image) was used to determine the height. In the southern hemisphere map below (2nd image), the surface ranges from lows of minus 23.65 miles (38.06 kilometers) to 26.61 miles (42.82 kilometers).

The shape model was constructed using images from Dawn’s framing camera that were obtained from July 17, 2011, to Aug. 26, 2012. The data have been stereographically projected on a 300-mile-diameter (500-kilometer-diameter) sphere with the poles at the center.

Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Newly Found Truck-Sized Asteroid to Whiz by Earth June 8

A truck-sized asteroid just discovered yesterday (Thursday, June 6) will give Earth a relatively close shave later today/early tomorrow, depending on your time zone. Asteroid 2013 LR6 is somewhere between 5- 16 meters (16 to 54 feet) in diameter and will be flying by at only about 111,000 kilometers (69,000 mi, 0.29x Lunar Distances) from Earth at 4:43UTC/12:43AM EDT on June 8, 2013.
This is similar in size to the space rock that exploded over Russia back in February of this year. The Russian asteroid was about 15 meters (50 feet) in diameter before it exploded in an airburst event about 20-25 km (12-15 miles) above Earth’s surface.
Find out how you can watch the flyby live online, below. This flyby is not at close as February’s 2012 DA14 flyby, but it indeed is quite close on by Solar System standards. It will be speeding by 9.8 km a second (6.14 mi/s). The asteroid was first spotted by the Catalina Sky Survey and now several other observatories have made follow-up observations to verify and help determine its size and orbit.


According to the Minor Planet Center’s Twitter feed, 2013 LR6 is the 167th minor planetary object discovered so far in the month of June 2013! That is incredible, and as astronomer Nick Howes said via Twitter, “That number should give people a good heads up as to why searching is important.”
According to our David Dickinson, 2013 LR6 will be plunging thru the constellation Vela at closest approach tonight, but it will be a faint one, as it won’t break +13 magnitude.
Since this discovery is so new, the Gianluca Masi an the Virtual Telescope Project in Italy has put together a last-minute opportunity to watch the flyby live, online via their telescopes.
The online event is scheduled for June 7, 2013 at 21:30 UTC. To watch, go to the Virtual Telescope project’s webcast page. 

Credit: Nancy Atkinson

Newly Found Truck-Sized Asteroid to Whiz by Earth June 8

A truck-sized asteroid just discovered yesterday (Thursday, June 6) will give Earth a relatively close shave later today/early tomorrow, depending on your time zone. Asteroid 2013 LR6 is somewhere between 5- 16 meters (16 to 54 feet) in diameter and will be flying by at only about 111,000 kilometers (69,000 mi, 0.29x Lunar Distances) from Earth at 4:43UTC/12:43AM EDT on June 8, 2013.

This is similar in size to the space rock that exploded over Russia back in February of this year. The Russian asteroid was about 15 meters (50 feet) in diameter before it exploded in an airburst event about 20-25 km (12-15 miles) above Earth’s surface.

Find out how you can watch the flyby live online, below.

This flyby is not at close as February’s 2012 DA14 flyby, but it indeed is quite close on by Solar System standards. It will be speeding by 9.8 km a second (6.14 mi/s). The asteroid was first spotted by the Catalina Sky Survey and now several other observatories have made follow-up observations to verify and help determine its size and orbit.

According to the Minor Planet Center’s Twitter feed, 2013 LR6 is the 167th minor planetary object discovered so far in the month of June 2013! That is incredible, and as astronomer Nick Howes said via Twitter, “That number should give people a good heads up as to why searching is important.”

According to our David Dickinson, 2013 LR6 will be plunging thru the constellation Vela at closest approach tonight, but it will be a faint one, as it won’t break +13 magnitude.

Since this discovery is so new, the Gianluca Masi an the Virtual Telescope Project in Italy has put together a last-minute opportunity to watch the flyby live, online via their telescopes.

The online event is scheduled for June 7, 2013 at 21:30 UTC. To watch, go to the Virtual Telescope project’s webcast page.

Credit:

"Now, for the first time in its billions of years of history, our planet is protected by far-seeing sentinels, able to anticipate danger from the distant future – a comet on a collision course, or global warming–and devise schemes for doing something about it. The planet has finally grown its own nervous system: us." 
- Daniel Dennett ( We Earth Neurons )

 

"Now, for the first time in its billions of years of history, our planet is protected by far-seeing sentinels, able to anticipate danger from the distant future – a comet on a collision course, or global warming–and devise schemes for doing something about it. The planet has finally grown its own nervous system: us."

- Daniel Dennett ( We Earth Neurons )

 

Trojans and Hildas

Here are some asteroids viewed in a rotating frame of reference where Jupiter almost stands still. The Trojans, in green, are asteroids that stay near the Lagrange points 60° ahead or behind Jupiter.  They go around the Sun once each time Jupiter orbits the Sun.  But the Hildas, in purple, go around the Sun 3 times while Jupiter goes around twice.  We say they’re in a 3:2 resonance with Jupiter. 
The Hildas seem to be moving in a triangular pattern.  But actually each one takes an elliptical orbit around the Sun.  There are three kinds of ellipses. Two go farthest from the Sun near the Lagrange points, while one goes farthest from the Sun opposite Jupiter.  Although the whole triangle of Hildas is nearly equilateral, it’s not quite.  The side between the two Lagrange points is a bit different from the two other sides.   You can also see the whole triangle pulsing as Jupiter moves in and out!
These animated gifs were made by Petr Scheirich, and you can have hours of fun looking at his website: http://sajri.astronomy.cz/asteroidgroups/groups.htmThere’s a lot to say about Trojans and Lagrange points, but let me talk about Hildas. Over 1,100 Hildas have been found, the being Hilda, named after the discoverer’s daughter.  It’s big - 175 kilometers in diameter - but not very bright, because it’s made of ancient stuff containing lots of carbon, similar to the nucleus of a comet.
The Hildas don’t form a ‘true’ asteroid family, because they aren’t fragments of a single parent object.  Instead, they’re a ‘dynamical’ family: they’re defined by having similar orbits.    Any Hilda’s orbit has an eccentricity less than 0.3, an inclination less than 20°, and a semi-major axis between 3.7 AU and 4.2 AU.  Remember, the semi-major axis of an ellipse is half the distance between the farthest points.So, the Hildas are outside the main asteroid belt, which lies between the 4:1 resonance with Jupiter at 2.1 AU and the 2:1 resonance at 3.0 AU.
The density of Hildas near the triangle’s corners is more than twice the density on the sides. The reason is that the Hildas move more slowly when they’re farther from the Sun!   So, they stay near the corners for an average of 5.0-5.5 years, but move along the sides of the triangle more quickly, for 2.5 to 3.0 years. The overall period of the Hildas is about 7.9 years, which is 2/3 the period of Jupiter.

Credit: John Baez, Petr Scheirich

Trojans and Hildas

Here are some asteroids viewed in a rotating frame of reference where Jupiter almost stands still. The Trojans, in green, are asteroids that stay near the Lagrange points 60° ahead or behind Jupiter.  They go around the Sun once each time Jupiter orbits the Sun.  But the Hildas, in purple, go around the Sun 3 times while Jupiter goes around twice.  We say they’re in a 3:2 resonance with Jupiter. 



The Hildas seem to be moving in a triangular pattern.  But actually each one takes an elliptical orbit around the Sun.  There are three kinds of ellipses. Two go farthest from the Sun near the Lagrange points, while one goes farthest from the Sun opposite Jupiter.  Although the whole triangle of Hildas is nearly equilateral, it’s not quite.  The side between the two Lagrange points is a bit different from the two other sides.   You can also see the whole triangle pulsing as Jupiter moves in and out!

These animated gifs were made by Petr Scheirich, and you can have hours of fun looking at his website: http://sajri.astronomy.cz/asteroidgroups/groups.htm

There’s a lot to say about Trojans and Lagrange points, but let me talk about Hildas. Over 1,100 Hildas have been found, the being Hilda, named after the discoverer’s daughter.  It’s big - 175 kilometers in diameter - but not very bright, because it’s made of ancient stuff containing lots of carbon, similar to the nucleus of a comet.



The Hildas don’t form a ‘true’ asteroid family, because they aren’t fragments of a single parent object.  Instead, they’re a ‘dynamical’ family: they’re defined by having similar orbits.    Any Hilda’s orbit has an eccentricity less than 0.3, an inclination less than 20°, and a semi-major axis between 3.7 AU and 4.2 AU.  Remember, the semi-major axis of an ellipse is half the distance between the farthest points.

So, the Hildas are outside the main asteroid belt, which lies between the 4:1 resonance with Jupiter at 2.1 AU and the 2:1 resonance at 3.0 AU.



The density of Hildas near the triangle’s corners is more than twice the density on the sides. The reason is that the Hildas move more slowly when they’re farther from the Sun!   So, they stay near the corners for an average of 5.0-5.5 years, but move along the sides of the triangle more quickly, for 2.5 to 3.0 years. The overall period of the Hildas is about 7.9 years, which is 2/3 the period of Jupiter.

Credit: , Petr Scheirich

(Source: Wikipedia)