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!
This animated gif is one of many made by Petr Scheirich, and you can have hours of fun looking at his website:
• Petr Scheirich, Asteroid (and comet) groups, 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.
Jupiter’s Trojan Asteroids Show Their True Colors
Scientists using data from NASA’s Wide-field Infrared Survey Explorer, or WISE, have uncovered new clues in the ongoing mystery of the Jovian Trojans — asteroids that orbit the Sun on the same path as Jupiter. Like racehorses, the asteroids travel in packs, with one group leading the way in front of the gas giant, and a second group trailing behind.
The observations are the first to get a detailed look at the Trojans’ colors: both the leading and trailing packs are made up of predominantly dark, reddish rocks with a matte, non-reflecting surface. What’s more, the data verify the previous suspicion that the leading pack of Trojans outnumbers the trailing bunch.
The new results offer clues in the puzzle of the asteroids’ origins. Where did the Trojans come from? What are they made of? WISE has shown that the two packs of rocks are strikingly similar and do not harbor any “out-of-towners,” or interlopers, from other parts of the Solar System. The Trojans do not resemble the asteroids from the main belt between Mars and Jupiter, nor the Kuiper belt family of objects from the icier, outer regions near Pluto.
“Jupiter and Saturn are in calm, stable orbits today, but in their past, they rumbled around and disrupted any asteroids that were in orbit with these planets,” said Tommy Grav, a WISE scientist from the Planetary Science Institute in Tucson, Ariz. “Later, Jupiter re-captured the Trojan asteroids, but we don’t know where they came from. Our results suggest they may have been captured locally. If so, that’s exciting because it means these asteroids could be made of primordial material from this particular part of the Solar System, something we don’t know much about.” Grav is a member of the NEOWISE team, the asteroid-hunting portion of the WISE mission.
The first Trojan was discovered on Feb. 22, 1906, by German astronomer Max Wolf, who found the celestial object leading ahead of Jupiter. Christened “Achilles” by the astronomer, the roughly 220- mile-wide (350-kilometer-wide) chunk of space rock was the first of many asteroids detected to be traveling in front of the gas giant. Later, asteroids were also found trailing behind Jupiter. The asteroids were collectively named Trojans after a legend, in which Greek soldiers hid inside in a giant horse statue to launch a surprise attack on the Trojan people of the city of Troy.
“The two asteroid camps even have their own ‘spy,’” said Grav. “After having discovered a handful of Trojans, astronomers decided to name the asteroid in the leading camp after the Greek heroes and the ones in the trailing after the heroes of Troy. But each of the camps already had an ‘enemy’ in their midst, with asteroid ‘Hector’ in the Greek camp and ‘Patroclus’ in the Trojan camp.”
Other planets were later found to have Trojan asteroids riding along with them too, such as Mars, Neptune and even Earth, where WISE recently found the first known Earth Trojan.
Before WISE, the main uncertainty defining the population of Jupiter Trojans was just how many individual chunks were in these clouds of space rock and ice leading Jupiter, and how many were trailing. It is believed that there are as many objects in these two swarms leading and trailing Jupiter as there are in the entirety of the main asteroid belt between Mars and Jupiter.
To put this and other theories to bed requires a well-coordinated, well-executed observational campaign. But there were many things in the way of accurate observations — chiefly, Jupiter itself. The orientation of these Jovian asteroid clouds in the sky in the last few decades has been an impediment to observations. One cloud is predominantly in Earth’s northern sky, while the other is in the southern, forcing ground-based optical surveys to use at least two different telescopes. The surveys generated results, but it was unclear whether a particular result was caused by the problems of having to observe the two clouds with different instruments, and at different times of the year.
Enter WISE, which roared into orbit on Dec. 14, 2009. The spacecraft’s 16-inch (40-centimeter) telescope and infrared cameras scoured the entire sky looking for the glow of celestial heat sources. From January 2010 to February 2011, about 7,500 images were taken every day. The NEOWISE project used the data to catalogue more than 158,000 asteroids and comets throughout the Solar System.
“By obtaining accurate diameter and surface reflectivity measurements on 1,750 Jupiter Trojans, we increased by an order of magnitude what we knew about these two gatherings of asteroids,” said Grav. “With this information, we were able to more accurately than ever confirm there are indeed almost 40 percent more objects in the leading cloud.”
Trying to understand the surface or interior of a Jovian Trojan is also difficult. The WISE suite of infrared detectors was sensitive to the thermal glow of the objects, unlike visible-light telescopes. This means WISE can provide better estimates of their surface reflectivity, or albedo, in addition to more details about their visible and infrared colors (in astronomy “colors” can refer to types of light beyond the visible spectrum).
“Seeing asteroids with WISE’s many wavelengths is like the scene in ‘The Wizard of Oz,’ where Dorothy goes from her black-and-white world into the Technicolor land of Oz,” said Amy Mainzer, the principal investigator of the NEOWISE project at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Because we can see farther into the infrared portion of the light spectrum, we can see more details of the asteroids’ colors, or, in essence, more shades or hues.”
The NEOWISE team has analyzed the colors of 400 Trojan asteroids so far, allowing many of these asteroids to be properly sorted according to asteroid classification schemes for the first time.
“We didn’t see any ultra-red asteroids, typical of the main belt and Kuiper belt populations,” said Grav. “Instead, we find a largely uniform population of what we call D-type asteroids, which are dark burgundy in color, with the rest being C- and P-type, which are more grey-bluish in color. More research is needed, but it’s possible we are looking at the some of the oldest material known in the Solar System.”
Scientists have proposed a future space mission to the Jupiter Trojans that will gather the data needed to determine their age and origins. Studying the Jupiter Trojans could provide astrobiologists with important information about how the Solar System has evolved over time, and the conditions that led Earth to become a habitable planet.
The results were presented at the 44th annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nev. Two studies detailing this research are accepted for publication in the Astrophysical Journal.
Source: JPL press release
The Mystery of the Zodiacal Light
Zodiacal light—the faint white glow that stretches across the darkest skies, tracing the same path the sun takes—has mystified scientists for centuries. They’ve known that it is sunlight reflected from a disk of dust spanning the inner solar system from Mercury to Jupiter. They just didn’t know where the dust came from—until now.
Every day, Earth sweeps up about 140 tons of cosmic dust. The particles are mostly 100 micrometers to 200 micrometers in size and made of silicate minerals. Most burn up in the atmosphere, although some survive and end up in micrometeorite collections. To figure out how this dust behaves in the inner solar system, planetary dynamicist David Nesvorný of Southwest Research Institute in Boulder, Colorado, and five colleagues set up a computer model. In addition to being subject to the tug of planetary gravity, microscopic particles orbiting the sun are pushed outward by the pressure of sunlight, dragged inward by their own radiative emissions, and worn down by collisions with other particles. Nesvorný and his colleagues followed particles released in their model from various types of comets or from asteroids and compared the particles’ fates with observations of the zodiacal dust cloud.
Previous studies had suggested that much of the zodiacal light came from the dust of colliding asteroids, but the only way this model could reproduce the great breadth of the zodiacal cloud above and below the plane of the planets was to have the dust come from the comets that orbit in the vicinity of Jupiter’s orbit. Those comets already range much farther from the plane of the planets than asteroids do, and Jupiter’s gravitational effects would drive their dust even farther afield. To make the modeled zodiacal cloud as dense as the real one, the dust had to come from comets falling apart, not just those shedding dust near the sun, the team reports in the 20 April issue of The Astrophysical Journal.
The new modeling has “produced a detailed and convincing case that [90% of] interplanetary dust particles and the hundreds of particles that are now curated on Earth originate from Jupiter family comets,” writes planetary scientist Stanley Dermott of the University of Florida, Gainesville, in an e-mail. Comets throw up the dust veil that creates the zodiacal light, and they supply most of the micrometeorites studied on Earth. Massive numbers of comets may even produce the bright debris disks seen around other stars. Now if only light-polluted skies didn’t deny most people a view of comets’ death glow.
Credit: Andrew Blanchard, David Nesvorný and Peter Jenniskens/SWRI/SETI Institute; (inset) Dominic Cantin
NASA is planning for a robotic spaceship to lasso a small asteroid and park it near the moon for astronauts to explore
The robotic ship would capture the 500-ton 25-foot asteroid in 2019. Then using an Orion space capsule, now being developed, a crew of about four astronauts would nuzzle up next to the rock in 2021 for spacewalking exploration, according to a government document obtained by The Associated Press.
Yay!
April/6/2013, 6pm
with 308 NotesReblog |
Senator says NASA to lasso asteroid, bring it closer (Update)
NASA is planning for a robotic spaceship to lasso a small asteroid and park it near the moon for astronauts to explore, a top U.S. senator disclosed Friday. The robotic ship would capture the 500-ton 25-foot (450 metric ton, 7.6 meters) asteroid in 2019. Then using an Orion space capsule, now being developed, a crew of about four astronauts would nuzzle up next to the rock in 2021 for spacewalking exploration, according to a government document obtained by The Associated Press. Sen. Bill Nelson said the plan would speed up by four years the existing mission to land astronauts on an asteroid by bringing the space rock closer to Earth. Nelson, a Democrat who is chairman of the Senate science and space subcommittee, said Friday that President Barack Obama is putting $100 million in planning money for the accelerated asteroid mission in the 2014 budget that comes out next week. The money would be used to find the right small asteroid. “It really is a clever concept,” Nelson said in a news conference in Florida the state where NASA launches take place. “Go find your ideal candidate for an asteroid. Go get it robotically and bring it back.”
In this Jan. 13, 2013 file photo (above), the Orion Exploration Flight Test 1crew module is seen in the Operations and Checkout building during a media tour at the Kennedy Space Center in Cape Canaveral, Fla. Senate Science and Space subcommittee Chairman Sen. Bill Nelson, D-Fla. says President Barack Obama and NASA are planning for a robotic spaceship to lasso a small asteroid and park it near the moon. Then astronauts would explore it in 2021. Nelson said the plan would speed up by four years an existing mission to land astronauts on an asteroid by bringing the space rock closer to Earth. (AP Photo/John Raoux)
While there are thousands of asteroids that size out there, finding the right one that comes by Earth at just the right time to be captured will not be easy, said Donald Yeomans, who heads NASA’s Near Earth Object program that monitors close-by asteroids. He said once a suitable rock is found it would be captured with the space equivalent of “a baggie with a drawstring. You bag it. You attach the solar propulsion module to de-spin it and bring it back to where you want it.” Yeomans said a 25-foot asteroid is no threat to Earth because it would burn up should it inadvertently enter Earth’s atmosphere. The mission as Nelson described is perfectly safe, he said. Nelson said this would help NASA develop the capability to nudge away a dangerous asteroid if one headed to Earth in the future. It also would be training for a future mission to send astronauts to Mars in the 2030s, he said. The government document said the mission, with no price tag at the moment, would inspire because it “will send humans farther than they have ever been before.”
April/6/2013, 1pm
with 64 NotesReblog |
The strangest asteroid that astronomers had ever seen
Sometimes the line separating “asteroid” from “comet” is a blurry one. For instance, there is the strange asteroid Chiron. Discovered in 1979 by astronomer Charles T. Kowal, it was cataloged as asteroid number 2060. But almost immediately, it was recognized as being a little weird.
First, because its orbit turned out to lie between Uranus and Saturn…much further from the sun than any other asteroid. It also had the strange habit of seeming to change its brightness. In 1988, astronomers William Hartmann, Dave Tholen and Dale Cruikshank noticed that Chiron was nearly twice as bright as it was supposed to be. The asteroid continued to brighten, eventually becoming three times brighter than usual. What was going on?
The answer was that Chiron contains a lot of ice and as its orbit carried it closer to the sun, some of this ice turned to gas. A huge cloud of gas and dust was forming around the asteroid. In effect, Chiron had turned into a comet.
Then, astronomers observed an event recently that was similar but even more spectacular…
It was discovered by the Lincoln Near Earth Asteroid Research (LINEAR). This is an MIT project jointly funded by the United States Air Force and NASA. One of its goals is to detect and catalog near-earth asteroids that might potentially threaten the Earth.
On January 6 it found an object that was cataloged as P/2010 A2. This turned out to be something so unusual that last week the Hubble Space Telescope was focused on it. What Hubble revealed is an object that is almost completely unique. At first glance, it seemed to be comet. But the 460-foot nucleus was offset from the tail, which had a very unusual structure near the nucleus. And there was no discernable gas in the tail. Since P/2010 A was located in the asteroid belt, scientists are speculating that it may be the result of a collision between two asteroids. Such a collision would have occurred at over 9000 miles per hour—-five times the speed of a rifle bullet. This would have released energy equivalent to an atomic bomb, creating a cloud of dust and debris. This cloud was then blown by the pressure of sunlight into a long, trailing comet-like tail
P/2010 A gives scientists a glimpse into the early history of our solar system, when similar collisions between planetesimals eventually created the planets we know today—-including our own earth.
Credit: Ron Miller
Has NASA Become Mars-Obsessed?
The landing of the Curiosity rover was a huge hit for nasa in the summer of 2012. Now the space agency is letting its winnings ride with another bet on Mars. Last December, NASA announced plans to send a similar rover to the Red Planet in 2020—its seventh planned or active Mars mission—citing the low risk and cost savings of a mission reboot.
NASA’s fixation on Mars (or on avoiding risks) comes at the expense of the rest of the solar system. Outer planets Uranus and Neptune have scarcely been explored. The same goes for Jupiter’s moon Europa, which planetary scientists believe to be a promising habitat for extraterrestrial life.
Recently a team of researchers proposed a novel mission concept: a floating spacecraft that would explore the hydrocarbon seas of Saturn’s moon Titan. But NASA opted instead for a Mars lander called InSight—which, like the 2020 rover, is a low-risk mission based on proved hardware.
For interactive graphics about planetary exploration, see ScientificAmerican.com/mar2013/graphic-science
March/2/2013, 11pm
with 84 NotesReblog |
In this movie, strung together from a series of images provided by the framing camera on NASA’s Dawn spacecraft, we see a full rotation of Vesta, which occurs over the course of roughly five hours.
Credit: JPL
Asteroid 2012 DA14 – Earth Flyby Reality Check
Small near-Earth asteroid 2012 DA14 will pass very close to Earth on February 15, so close that it will pass inside the ring of geosynchronous weather and communications satellites. NASA’s Near-Earth Object Program Office can accurately predict the asteroid’s path with the observations obtained, and it is therefore known that there is no chance that the asteroid might be on a collision course with Earth. Nevertheless, the flyby will provide a unique opportunity for researchers to study a near-Earth object up close. Here are the facts about the safe flyby of Earth of asteroid 2012 DA14 — a record close approach for a known object of this size.
These real-time simulations depict asteroid 2012 DA14 in its orbit around the sun and provide the asteroid’s current distance from Earth. 2012 DA14 will have a close, but safe, pass by Earth on Feb. 15, 2013 at 2:25 p.m. EST (19:25 UTC). At that time, the asteroid will pass no closer than 17,000 miles above the surface of Earth over Indonesia. The simulations, created with NASA’s Eyes on the Solar System, refresh every two minutes.
Click here to watch the real-time simulations
Credit: NASA
Stranger in the Night: Space Rock to Make Close Earth Flyby
A little-known asteroid will skim past Earth on 15 February, passing just 28 000 km from our planet. The 50 m-diameter chunk of space rock was discovered in last year by ESA-sponsored amateur astronomers in Spain.
Details of the ancient asteroid, 2012 DA14, are sketchy – no direct measurements of its size are available. From its brightness, scientists estimate its diameter at 50–80 m. Its composition is unknown and its mass is thought to be of the order of 130 000 tonnes.
What is known is that it will not impact Earth anytime soon.
Credit: ESO
In Two Weeks This 50-Meter Asteroid Will Buzz Our Planet
On February 15 a chunk of rock about 50 meters wide will whiz by Earth at nearly 8 km/s, coming within 27,680 km of our planet’s surface — closer than many weather and communications satellites.
For those of you more comfortable with imperial units, that’s 165 feet wide traveling 17,800 mph coming within 17,200 miles. But regardless whether you prefer meters or miles, in astronomy that’s what’s called a close call.
Scientists stress that there’s no danger of an impact by this incoming asteroid, designated 2012-DA14, but it’s yet another reminder that in our neck of the Solar System we are definitely not alone.
“2012-DA14 will definitely not hit Earth,” says JPL’s near-Earth object specialist Don Yeomans. “The orbit of the asteroid is known well enough to rule out an impact.”
But with 2012-DA14′s upcoming February flyby Yeomans notes, “this is a record-setting close approach.”
The rocky asteroid will come within about 4 Earth radii, which is well within the orbits of geosynchronous satellites. During its closest approach at 19:26 UTC it should be visible in the sky to amateur telescopes (but not the naked eye), becoming as bright as an 7th- or 8th-magnitude star.
Radar observatories will be watching 2012-DA14 during the days leading up to and following its approach in an attempt to better determine its size, shape and trajectory. NASA’s Goldstone facility will have an eye — er, dish — on DA14, but it won’t be visible to Arecibo. Stay tuned for more info!
Read more about 2012-DA14 on the JPL Near-Earth Object Program page here.
New Asteroid Mining Company Aims to Manufacture Products in Space
A new private company called Deep Space Industries announced today that it intends to send a fleet of small spacecraft to near-Earth asteroids with the aim of mining resources and turning them into products using space-based 3-D printers.
Last year was thick with audacious private spaceflight company unveilings, including the announcement from Planetary Resources, Inc. of their plans to mine relatively valuable platinum group metals from asteroids. With the formation of Deep Space Industries, it seems that 2013 could see a new crop of private space companies with lofty goals.
“We are about prospecting, exploring, harvesting, extracting, and manufacturing based on the resources of space,” said Rick Tumlinson, founder and chairman of DSI, during a press conference on Jan. 22. Tumlinson has been an ardent space advocate for many years, helping found MirCorp, which brought space tourist Dennis Tito to the International Space Station.
There exists potentially extremely valuable material on asteroids, including nickel, silicon, platinum group metals such as platinum and palladium, and water, which can be broken down into hydrogen and oxygen to make rocket fuel. DSI intends to create a fleet of prospecting spacecraft called “FireFlies” (perhaps trying to rouse interest in their plans from Joss Whedon acolytes) that will travel to asteroids in Earth’s vicinity on journeys of two to six months. The spacecraft will be built up from teams of small CubeSats — low-cost miniature satellites — to form 25 kg (55 lbs) machines that can collect data about the best asteroids to mine from. The company hopes to launch the first FireFly in 2015.
NASA, ESA Telescopes Find Evidence for Asteroid Belt Around Vega
Astronomers have discovered what appears to be a large asteroid belt around the star Vega, the second brightest star in northern night skies. The scientists used data from NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory, in which NASA plays an important role.
The discovery of an asteroid belt-like band of debris around Vega makes the star similar to another observed star called Fomalhaut. The data are consistent with both stars having inner, warm belts and outer, cool belts separated by a gap. This architecture is similar to the asteroid and Kuiper belts in our own solar system.
What is maintaining the gap between the warm and cool belts around Vega and Fomalhaut? The results strongly suggest the answer is multiple planets. Our solar system’s asteroid belt, which lies between Mars and Jupiter, is maintained by the gravity of the terrestrial planets and the giant planets, and the outer Kuiper belt is sculpted by the giant planets.
“Our findings echo recent results showing multiple-planet systems are common beyond our sun,” said Kate Su, an astronomer at the Steward Observatory at the University of Arizona, Tucson. Su presented the results Tuesday at the American Astronomical Society meeting in Long Beach, Calif., and is lead author of a paper on the findings accepted for publication in the Astrophysical Journal.
