We recently looked at JAXA's planned solar sail mission to Jupiter (see JAXA Sail to Jupiter's Trojan Asteroids), but I want to come back around to the Trojans this morning in light of a discovery announced today. The more we learn about the Trojans, the better. Most appear to be class D asteroids, dark with reddish hues and probably covered in tholins, organic polymers that result from the solar irradiation of organic compounds. Tholins show up all over the place in the outer system's icy objects, adding to the view that the Jupiter Trojans were probably captured into their present orbits during the early days of Solar System formation. Asteroid 2015 BZ509, discovered by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in 2015, turns out to be a Trojan with a difference. Revealed in the current issue of Nature by discoverers Paul Wiegert (Western University, London), Martin Connors (Athabasca University, CA) and Christian Veillet (Large Binocular Telescope...

Learning about the changes that occur on a cometary surface over time was a primary goal of the European Space Agency's Rosetta mission, which orbited comet 67P/Churyumov-Gerasimenko between August 2014 and September 2016. This was a period when the comet was swinging through the inner Solar System as it closed to perihelion. Now we have vivid evidence of the changes the comet experienced as recorded by Rosetta. Consider a report in Nature Astronomy, which chronicles outburst activity on the comet associated with the spectacular collapse of a cliff face. Located in the Seth region of the comet on a prominent cliff edge was a 70-meter long fracture about 1 meter wide. During the period of observation, as Rosetta drew ever nearer perihelion, buried ices turned to vapor at an increasing rate, pulling dust out into space, with occasional outburst activity. Rosetta observed an outburst on July 10, 2015 that was associated with this region. Image: Comet cliff collapse before and after....

Among the five finalists for NASA's Discovery program, I had become attached to the Near Earth Object Camera (NEOCam), whose purpose was to expand our catalog greatly, with the potential, according to mission backers, of finding ten times more NEOs than we've found to date. We'll see if NEOCam has a future (I've just learned that it has been given extended funding for an additional year by NASA), but for now NASA has announced two other Discovery-class missions, both of which have objectives among the asteroids. Lucy, scheduled for a launch in the fall of 2021, is to be a robotic mission with the goal of exploring six of the Jupiter Trojan asteroids. The Trojans share Jupiter's orbit while moving swarm-like around the planet's L4 and L5 Lagrangian points. Over 6000 Jupiter Trojans are now known, but the population is thought to be vast, with as many as 1 million Trojans larger than 1 kilometer in diameter. As to their origin, there is much to learn. They may be captured asteroids or...

Years ago at the Aosta conference on interstellar studies, Greg Matloff told attendees about an interesting way to travel the Solar System. If the goal is to get to Mars, for example, it turns out that there are two objects -- 1999YR14 and 2007EE26 -- that pass close to both Earth and Mars, each with transit time of about a year. Let me quote from Greg's paper: Since orbital characteristics are known for a few thousand NEOs, it is reasonable to assume that about 0.1% of the total NEO population could be applied for Earth-Mars or Mars-Earth transfers during the time period 2020-2100. Because a few hundred thousand NEOs must exist that are greater in dimension than 10m, hundreds of small NEOs must travel near-Hohmann trajectories between Earth and Mars or Mars and Earth. It seems likely that a concerted search will find one or more candidate NEOs for shielding application during any opposition of the two planets. The notion is provocative. Could we somehow hitch a ride on one of these...

The so-called 'trojan' asteroids that cluster at 60° ahead and behind the planet Jupiter make up a surprisingly populous category. Consider that thus far we have found only one trojan at Earth's Lagrangian points, while over 6000 have been discovered in Jupiter's orbit. The total number of trojans larger than 1 km in diameter associated with Jupiter has been estimated to be about 1 million, which matches up well with objects of equivalent size in the main asteroid belt. These days 'trojans' can also refer to similar bodies associated with other planets. We know, for example, of about 20 trojans involved with Neptune. That solitary Earth trojan, 2010 TK7, was discovered oscillating around Earth's L4 Lagrangian point in 2010 by the NEOWISE team using NASA's Wide-field Infrared Survey Explorer spacecraft. The object has a diameter of about 300 meters; its oscillations take it back and forth on a nearly 400 year cycle that at times puts it close to opposite the Sun with respect to...

A mission as complex as the European Space Agency's highly successful Rosetta is a compilation of interlocking parts. I always find it fascinating to look at the instrumentation aboard. Take Alice, a UV imaging spectrograph no bigger than a shoebox. Alice weighs in at less than 4 kilograms and draws a meager 4 watts of power, but it offered us a thousand times the data we could retrieve with similar instruments no more than a generation ago. Alice produced over 70,000 spectra in two years, according to its principal investigator, Alan Stern (a familiar name indeed for those interested in the outer Solar System!) With these data we're learning about the porous surface of the comet, its lack of exposed water ice, and the unexpected occurrence of molecular hydrogen around it. Rosetta's Ion and Electron Spectrometer (IES), likewise the work of the Southwest Research Institute, is another triumph of miniaturization, achieving the sensitivity of instruments weighing five times as much (IES...

I've always thought that the biggest driver for our next steps in space is the presence of asteroids. Asteroids affect us in two powerful ways, the first being that they are sources of potential wealth for companies like Deep Space Industries and Planetary Resources, as commercial operations use robotics and eventually humans to extract water and precious metals. Likewise significant is that near-Earth asteroids are a reminder that developing the tools for altering an asteroid trajectory is a good insurance policy for planetary protection. Asteroids go past us all the time. I count eight that will move past the Earth between now and October 1, the closest -- 2015 SO2 and 2015 DS53 -- moving within 17 lunar distances. There's nothing to worry about in this list, as all have zero chance of impacting the Earth. Looking ahead to the first 20 days of October, the closest pass will be by asteroid 462959, at 15 lunar distances. A lunar distance is 384,401 kilometers, and it's how the Minor...

Comet 332P/Ikeya-Murakami has had a short but colorful history in our observations. First detected in 2010 by two amateur astronomers in Japan, the comet has been spinning off debris at least since 2015 and probably earlier. A large fragment, as big as Comet 332P itself, may have broken off in 2012. Still close to the comet, its discovery prompted a team led by David Jewitt (UCLA) to request time on the Hubble Space Telescope to study what was happening. Among a long page of posted quotations on Jewitt's UCLA website is this by Erwin Schrodinger: "The task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees." In this case, what everybody now sees is our most in-depth look at a comet's disintegration ever. The trick is what to make of what we see. The Hubble observations, taken in early 2016, show us 25 separate fragments, mixtures of dust and ice that are slowly separating from the comet at no more than the pace I...

We're only a month away from further excitement from Comet 67P/Churyumov-Gerasimenko. As the mission approaches its final days, the Rosetta orbiter will conclude its activities with a controlled descent to the region called Ma'at, an area of open pits on the comet's surface that may reveal information about its interior structure. The descent, which will occur on September 30, comes after the months of intense scrutiny that led to the location of the Philae lander. We did get data from Philae, but as you know, shortly after its initial touchdown at Agilkia, the lander bounced and continued to drift over the surface for another two hours. Its final location, on the comet's smaller lobe, was subsequently named Abydos. Philae's hibernation, after only three days, was the result of battery exhaustion, but the lander was able to communicate again with Rosetta in June and July of 2015 as the comet moved toward perihelion in August. Even then, controllers didn't know Philae's precise...

Back in the 1930s, the German astronomer Karl Reinmuth discovered a near-Earth asteroid now called 1862 Apollo, which gave its name to the Apollo asteroids, all of them Earth-crossing and of high interest to those looking to plan asteroid missions. The number of known Apollo asteroids totals close to 7000. The one that gains our attention today is 101955 Bennu, for this is the target of the upcoming OSIRIS-REx mission, scheduled for launch on September 8. Standing for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, OSIRIS-REx is a sample return mission that will, if all goes well, reach Bennu in 2018, surveying the asteroid from nearby space for 505 days in search of optimum sampling sites. The plan is for no actual landing but a very close approach in which the spacecraft's extended robotic arm will attempt to gather the sample. The robotic arm (known as TAGSAM, for Touch-And-Go Sample Acquisition Mechanism) will collect between 60 and 2,000...

Most readers will recall the Spacecoach, developed by Brian McConnell and Alex Tolley and widely discussed in these pages. A workhorse spacecraft designed to shuttle crew and cargo between Earth and nearby planets, the Spacecoach was presented as a way to open up regular commercial use of the Solar System, on the pattern of the stagecoaches that connected towns in the American Old West. One of the many beauties of the Spacecoach was the idea of using reclaimed water and waste gases as a propellant in its electric engines. With water as a propellant, the mass of the system can be sharply reduced, with an associated reduction in mission costs. Benefits like that don't stay hidden for long, and I see that Deep Space Industries is likewise attracted to water in the design of its new engine. The Prospector-1 spacecraft, slated for launch by the end of the decade, uses a system DSI calls 'Comet.' It expels superheated water to create thrust, a useful idea given the company's intentions....

Yesterday's post on the distribution of asteroid populations inevitably had me thinking about the Chelyabinsk event on February 15, 2013, and about the concurrent flyby of the asteroid (367943) Duende, which took place on the same day. A scant sixteen hours after the explosion of the Chelyabinsk bolide and the fall of five tons of meteoritic material to the ground in Siberia, (367943) Duende passed by at about 27,700 kilometers above the surface of the Earth. We talked yesterday about learning more about asteroid distributions, so we could understand where they come from and what to expect as we assess their trajectories. In the case of Chelyabinsk, it was originally thought that both events were related, with the Chelyabinsk impactor associated with (367943) Duende in the form of a companion object, or perhaps as material that broke away from the parent asteroid. But an analysis of the orbits of both objects as well as spectroscopic analysis of Duende and the Chelyabinsk material...

We know that understanding Near-Earth Objects is vital not only for assessing future asteroid surveys and spacecraft missions, but also for tracking potential impactors on Earth. Projects like the Catalina Sky Survey and its now defunct southern hemisphere counterpart, the Siding Spring Survey, are all about asteroid and comet discovery, with a more specific goal of looking for objects posing a potential hazard to our planet. We lost the Siding Spring effort in 2013 due to funding problems, but the Catalina Sky Survey (CSS) is still in robust operation. The survey draws data from a 1.5 meter telescope on the peak of Mt. Lemmon (Arizona) and a 68 centimeter instrument nearby at Mt. Bigelow. Now we have word that Mikael Granvik (University of Helsinki) and an international team of researchers have drawn on about 100,000 images acquired by the Catalina Sky Survey to study the properties of some 9000 NEOs detected in an eight-year period. The goal is to construct a model for the...

Back when I was in grade school, we put in several months studying ancient Egyptian culture. I can remember becoming fascinated with the pyramid builders and wanting to immerse myself in the world that produced them. But I don't think I ever reached the multidisciplinary level of a third-grader named Michael Puzio, who named the asteroid now called Bennu. The sharp-eyed Puzio entered a contest to name the asteroid that the OSIRIS-REx mission will fly to, choosing the Egyptian deity Bennu because he thought the spacecraft resembled the mythological bird. I call Michael Puzio one smart third-grader, and I'm happy that yesterday's post, on the near-Earth asteroid 2003 SD220, brought him to mind. The close pass by 2003 SD220 on Christmas Eve prompted a series of radar studies that we'll now use to help refine its orbit. Bennu is likewise nearby, though at about 500 meters a bit smaller than 2003 SD220, and it too has been the object of study by the planetary radars at Arecibo and...

An asteroid shaped something like a sweet potato swept by the Earth on December 24, though at a sufficient distance (28 times further away than the Moon) to pose no hazard to our planet. 2003 SD220 was making the first of five predicted encounters within the next twelve years, and the measurements made by the planetary radar system at Arecibo on the asteroid's shape, rotation and other properties will now be useful in refining its orbit. The Jet Propulsion Laboratory's Goldstone Solar System Radar and the National Radio Astronomy Observatory's Green Bank Telescope and Very Long Baseline Array also contributed data on the asteroid. Highly elongated and more than 2 kilometers long, 2003 SD220 is of interest as a possible target for a future space mission, not only because asteroids should give us clues about conditions in the early Solar System, but also because near-Earth asteroids need to be well understood in case we one day find ourselves dealing with a potential impactor. Image:...

Yesterday's post on what we're learning about Rosetta's comet (67P/Churyumov-Gerasimenko) briefly touched on the issue of changing the orbit of such bodies for use in resource extraction. Moving the comet Grigg-Skjellerup is part of the plot of Neal Stephenson's novel Seveneves, where the idea is to support a growing human population in space with the comet's huge reserves of water. Just how hard it would be to move a comet is made clear by how a proposed near-term mission approaches the question of deflecting a small asteroid. The mission, discussed at the ongoing European Planetary Science Congress in Nantes, is called AIDA, for Asteroid Impact and Deflection Assessment. A joint mission being developed by the European Space Agency and NASA, AIDA is actually a two-pronged affair. ESA is leading the Asteroid Impact Mission (AIM), while NASA is behind the Double Asteroid Redirection Test (DART). The plan is to rendezvous with the asteroid (65803) Didymos and its tiny satellite (known...

Just over a year from now, we'll be anticipating the launch of the OSIRIS-REx mission, scheduled to rendezvous with the asteroid Bennu in 2018. This will be the first American mission to sample an asteroid, and it's interesting to note that the materials scientists hope to return will constitute the largest sample from space since the days of Apollo. As with recent comet studies, asteroid investigations may give us information about the origin of the Solar System, and perhaps tell us something about sources of early water and organic materials. This NASA Goddard animation offers a fine overview of the target and the overall mission. [youtube gtUgarROs08 500 416] But OSIRIS-REx is about more than the early Solar System. Recent scare stories have compelled NASA to state that a different asteroid, sometimes identified as 2012 TT5, will not impact our planet in September of this year. As Colin Johnston points out in Astronotes (the blog of Armagh Planetarium), 2012 TT5 will, on the 24th...

With Rosetta's continuing mission at Comet 67P/Churyumov-Gerasimenko, now post-perihelion but continuing to gather data, comets and their role in the history of the Solar System stay very much on my mind. Their role as delivery mechanisms for volatiles to an infant Earth is widely investigated, as is the idea that comet impacts may be linked to some of the great extinction events. But perhaps nothing is as provocative as the idea that comets had a role in actually starting life on our planet, with obvious implications for the likelihood of life elsewhere. Image: This series of images of Comet 67P/Churyumov-Gerasimenko was captured by Rosetta's OSIRIS narrow-angle camera on 12 August 2015, just a few hours before the comet reached the closest point to the Sun along its 6.5-year orbit, or perihelion. The image at left was taken at 14:07 GMT, the middle image at 17:35 GMT, and the final image at 23:31 GMT. The images were taken from a distance of about 330 km from the comet. The comet's...

The last time we caught up with Wendy Panero's work, the Ohio State scientist was investigating, with grad student Cayman Unterborn, a possible way to widen the habitable zone. Slow radioactive decay in elements like potassium, uranium and thorium helps to heat planets from within and is perhaps a factor in plate tectonics. In 2012, Unterborn argued that planets with higher thorium content than the Sun would generate much more heat than the Earth, allowing a habitable zone with liquid water on the surface correspondingly farther out from the star. You can read about that work and its implications in Widening the Habitable Zone. I was reminded of it because Panero reported at the recent American Geophysical Union meeting on her latest direction, a study involving the formation of the Earth's water. Recall that analysis of data from the Rosetta probe implicated asteroids rather than comets as the main delivery mechanism for Earth's oceans (see Rosetta: New Findings on Cometary Water)....

The impact at Tunguska, Siberia on June 30,1908, evidently a small asteroid, devastated 1300 square kilometers, which works out to be the equivalent of a large metropolitan area. June 30, 2015 is thus an appropriate date to launch Asteroid Day, a global awareness campaign to put the issue of dangerous impacts in front of as many people as possible. An early December press conference at the London Science Museum, hosted by Lord Martin Rees, UK Royal Astronomer, announced the campaign and released a declaration of needed action: Employ the available technology to detect and track near-Earth asteroids that threaten human populations A rapid hundred-fold (100x) acceleration of the discovery and tracking of NEOs Global adoption of Asteroid Day on June 30, 2015, to heighten awareness of the asteroid hazard and our efforts to prevent future impacts The list of scientists, business leaders and artists behind the 100x Declaration, as it's being called, is an impressive one that includes Jill...