From the depths of space it came. Speeding towards Earth, it passed within 60 lunar distances before it was discovered by the Pan-STARRS telescope. It’s a small asteroid or comet, like many that pass near Earth, but this one began its journey in another star system. 

We know this not because it has unusual characteristics, but simply from the path of its orbit. Planets, asteroids and comets follow elliptical paths around the Sun, we can determine their orbital paths by measuring their speed and distance from the Sun over a period of time. Since their orbits are determined by gravity, we can use Newton’s gravitational law to figure out its path knowing its speed and position.

Because of the gravitational pull of the Sun, an object moves faster when it is closer to the Sun and slower when it is farther away. At its farthest distance from the Sun, an object doesn’t have enough speed to overcome the Sun’s gravitational pull, so its path curves toward the Sun to make another orbit. By measuring the speed of this particular object, named A/2017 U1, we can calculate how far it could travel from the Sun before turning back. What we found was that it’s moving so fast it will escape the Sun’s gravity. It will leave our solar system never to return.

This can sometimes happen to a comet or asteroid that formed in our solar system. An asteroid can make a close approach to a large planet like Jupiter, giving it a boost of speed that sends it hurtling out of the solar system. We use this effect with spacecraft such as Voyager and New Horizons, which are now on their way toward interstellar space. But that couldn’t have happened to A/2017 U1. The path of its orbit is almost perpendicular to the orbits of the planets, and it hasn’t passed near any of the large planets in our solar system. So it must have been moving fast when it entered our solar system.

We’ve long thought that interstellar comets and asteroids were possible. We’ve known that with the right gravitational boost comets and asteroids can leave our solar system on rare occasions, and it stands to reason that comets and asteroids in other star systems can occasionally leave theirs. Given time, some of them will eventually visit other stars. But this is the first confirmed example of an interstellar visitor.

The post An Interstellar Object Visits Our Solar System appeared first on One Universe at a Time.

Traditionally the difference between comets and asteroids is simple. Comets form tails of gas and dust when they are near the Sun, and asteroids do not. But as we’ve learned more about asteroids and comets we’ve found that things aren’t as clear cut. 

Comet tails are produced when “volatiles” such as water ice on the comet’s surface are sublimed by the Sun’s heat. This means comets must have surface ice, leading to the idea that they are “dirty snowballs.” Asteroids, on the other hand, were seen as dry rocky bodies, hence their lack of tails. On a basic level that’s true, and comets do tend to be more icy than asteroids. But comets can be quite rocky in composition, and asteroids can have plenty of icy volatiles. So sometimes a comet can appear much like an asteroid and an asteroid can have a comet-like tail.

A good example of this can be seen in the asteroid P/2016 J1. It was discovered in 2016 by Pan-STARRS, and was found to have two separate components (called A and B). These two objects have extremely similar orbits, meaning that they were once a single asteroid that was broken in two by a collision or gravitational interaction. Computer simulations of their orbits show that the asteroid likely split apart about six years ago. That would make it the youngest fragmented asteroid we know.

P/2016 J1 is in the asteroid belt, taking about 5.5 years to orbit the Sun. At its closest approach (perihelion), the asteroid is about twice as far from the Sun as Earth. Last year when it was near perihelion, the two parts of the asteroid started to become active and produced long dusty tails. In other words they looked like comets. This was probably caused by ice that was exposed by the fragmentation. Once heated by the Sun, they started to sublime and created the tails we could observe.

This doesn’t mean comets are simply broken asteroids. What it does demonstrate is that the interiors of asteroids can have lots of icy volatiles. They are just hidden by an asteroid’s the rocky exterior. So comets and asteroids can’t easily be divided into dirty snowballs and dry rocks. Instead it is more a matter of degree. Asteroids and comets are far more similar than we once thought.

Paper: Fernando Moreno, et al. The splitting of double-component active asteroid P/2016 J1 (PANSTARRS). arXiv:1702.03665 [astro-ph.EP] (2017)

The post More Than Meets The Eye appeared first on One Universe at a Time.

Traditionally the difference between comets and asteroids is that comets have tails and asteroids don’t. As we’ve studied comets and asteroids, however, we’ve found the aren’t so clearly divided. It is not simply a matter of comets being icy snowballs and asteroids being dry rocks. Nor is it simply a matter of having a tail. As we’ve seen, asteroids can form tails as they enter the inner solar system. Recently we’ve seen a comet that doesn’t have a tail, and it may hold important clues to the origin of our solar system.

The comet C/2014 S3 has been called a manx comet due to its lack of tail. It’s lack of tail indicates that it doesn’t have icy volatiles on its surface.  Based upon what little coma is has, it’s estimated it has about a millionth the surface volatiles of a typical comet, which makes it much more like an asteroid in composition.

Actual image of the manx comet (as opposed to the artist rendering above). Credit: University of Hawaii Institute for Astronomy

Given that it’s so dry and rocky, why call it a comet at all? It turns out its trajectory takes it from about twice the distance of Earth all the way out to the Oort cloud, so it has a distinctly comet-like trajectory. The fact that it has come from the Oort cloud with very little ice is actually quite interesting. If it had formed in the Oort cloud it should have plenty of ice and would definitely have a tail. So it’s most likely that this particular body formed in the inner solar system where most volatiles are boiled off, and then was thrown outward to the Oort cloud.

One model of the early solar system, known as the Nice model, actually predicts the existence of such manx comets. As the planets began to form, they shifted their orbits dramatically, causing some of the material from the inner solar system to be thrown to the distant regions of our solar system. The timing of this would affect the amount of volatiles the material still has. If we can find similar manx comets, we should be able not only to confirm models of the early solar system, but might be able to fine tune the sequence of events.

Paper: Karen J. Meech, et al. Inner solar system material discovered in the Oort cloud. Science Advances Vol 2, No. 4 (2016) DOI: 10.1126/sciadv.1600038

The post Manx Comet appeared first on One Universe at a Time.

On Monday amateur astronomer John Mckeon captured an unusual flash on the limb of Jupiter while he was filming the planet through a telescope. He posted the video on Reddit, wondering if it might be some sort of meteor or comet impact. It was soon confirmed that the flash was also observed by Gerrit Kernbauer. It does indeed appear to have been an impact event. 

Such impact events have been recorded before. Similar impacts were recorded by amateurs in 2010 and 2012. Because such events are unexpected, we rely upon the luck of observers. While such impacts happen fairly regularly, the only time we had a heads-up on an impact was when comet Shoemaker-Levy 9 impacted Jupiter under the watchful eye of Hubble and other telescopes.

Since comet and meteor impacts occur on Jupiter so regularly, it’s a commonly held idea that Jupiter actually protects Earth from comet collisions by deflecting them, or even colliding with them. But in fact Jupiter can deflect a comet toward us just as easily as it can away from us. So the role of Jupiter as Earth’s protector is still unclear, though it’s suspected that it did play a role in the early stages of our solar system.

The post Amateur Astronomers Capture Jupiter Impact appeared first on One Universe at a Time.

The Wow! signal is one of the great mysteries of radio astronomy.  It was detected in 1977 by the Big Ear radio telescope, and is so named because of its powerful signal. It’s origin is unclear, but one possible explanation is that is was an intentional signal from an alien intelligence.

Big Ear was a drift telescope, and used the rotation of the Earth to scan the sky for radio signals. It was designed to run for long periods autonomously as a way to scan the heavens. The Wow! signal came from a specific region of the sky, and emitted a strong signal at 21 cm wavelengths, which is an emission light produced by atomic hydrogen. It was observed for 72 seconds, which is how long it would take a specific point in the sky to drift across the range of the telescope.

One interesting aspect of the signal is that it doesn’t clearly originate from a known object. The area of the sky where the signal originated doesn’t have anything that would produce a strong hydrogen line. But new work suggests that back in 1977 there was something there, possibly two somethings.

Between the end of July 27 and mid August of 1977, two comets known as 266P/Christensen and P/2008 Y2 (Gibbs) were in the vicinity of the Wow! signal location. Comets are known to emit gas and dust, including monotomic hydrogen. So there may have been a hydrogen cloud in the region during that time. The Wow! signal was detected on August 15, 1977.

While this is not the definitive answer, it would explain some of the strange aspects about the signal, such as why later observations of the region didn’t detect any signal. Since the comets had moved on, any hydrogen cloud would have dispersed and any signal from it would have faded.

So there’s no need for aliens after all.

The post Was The Wow! Signal Due To A Comet? appeared first on One Universe at a Time.

Today the object 2015 TB145 will make a “close” flyby of Earth. It’s been nicknamed Spooky due to its Halloween arrival date, and we’re already starting to learn a few things about it.

Spooky was presumed to be an asteroid when it was discovered, but was unusual because of its high relative speed (35 km/s). Its orbit is also unusual, being more inclined away from the plane of the solar system than most asteroids. Its trajectory is more in line with comets, though Spooky has no indication of a coma or tail. But we’re now starting to get infrared data from NASA’s Infrared Telescope Facility (IRTF) in Hawaii and radio observations from Arecibo, which supports the idea that Spooky is a dead comet.

In particular, the infrared observations allow us to determine the brightness (albedo) of the comet. It’s albedo is about 0.06, which, though about as dark as asphalt, is actually brighter than most comets.  So it is likely an old comet that has lost all its volatiles (surface ice and such) and now looks more asteroid-like than comet-like at first glance.

The post Spooky The Dead Comet appeared first on One Universe at a Time.

Comets are frozen remnants from the formation of our solar system. They live on the outer edges of our solar system until some gravitational perturbation causes them to sweep near the Sun. Because they have been relatively undisturbed for most the Sun’s history, they provide an excellent window into the chemistry and composition of the early solar system. Which is why it’s interesting that ethyl alcohol has been observed in the tail of comet Lovejoy.

Lovejoy is a long-period comet, which means it’s probably originates from the Oort cloud, and hasn’t had time to become contaminated by material of the inner solar system. Finding ethyl alcohol streaming off such a comet is somewhat surprising. We’ve long known that alcohol is plentiful in space, but much of it is in the form of methyl alcohol, which is a simpler molecule than ethyl alcohol. In this case, it seems the more complex alcohol formed through surface chemistry interacting with ultraviolet light. The team also found quantities of glycolaldehyde, which is a simple sugar-like molecule, which also supports the surface chemistry idea.

Compounds such as these are necessary ingredients for life on Earth, so its possible that comets similar to Lovejoy could have seeded Earth with these molecules through early impacts. That’s still a bit speculative, but it now seems clear that both comets and meteorites contain such molecules, so its within the realm of possibility that they seeded Earth with the building blocks of life.

At the very least the observations of Lovejoy show that these molecules formed in our solar system early in its history.

Paper: Nicolas Biver, et al. Ethyl alcohol and sugar in comet C/2014 Q2 (Lovejoy). Science Advances, 23 Oct 2015

The post Alcohol In Comet Lovejoy Points To Early Chemistry appeared first on One Universe at a Time.

When the Rosetta spacecraft reached comet 67P/Churyumov–Gerasimenko, one of the striking features was its “rubber duck” shape with two distinct lobes. One of the questions it raised was whether the comet had simply eroded in its middle region, or whether it had formed from a low-speed collision. We now know the ducky comet was once two comets.

Surface structures point to a two-comet origin. Credit: ESA

Computer simulations have shown that low-speed collisions between comets can create a single comet similar to 67P, but other models show how comets can erode irregularly to create similar shapes. So there has been debate over which process formed 67P. But new work has verified the collision model by looking at the surface gravity of the comet. As a surface of a comet settles within its gravitational field, the surface will tend to be oriented perpendicular to the direction of gravity in the region. Imagine a pile of sand on Earth. It can have high or low points in the sand, but if you jostle it, the sand will tend to level off. Not all surfaces will line up to gravity, but statistically most will.

So the team looked at several surface structures on 67P and compared them to the gravitational map to find a statistical correlation between the surface gravity. They then compared the results to two computer models. One where the comet eroded in the center, and one where two comets merged. What they found was that the real 67P agreed with the merged model.

So the one comet we’ve actually landed a probe upon was once two.

Paper: Jutzi and Asphaug. The shape and structure of cometary nuclei as a result of low-velocity accretion. Science 348 (6241): 1355-1358 (2015)

The post The Comet That Was Once Two appeared first on One Universe at a Time.

Comets are known for their tails. In the old days that’s how you distinguished a comet from an asteroid, though with our modern understanding the line between comet and asteroid as blurred a bit.  Still, one of the big areas of comet research has been on just how comet tails and coma form.

The traditional view has been that water and other volatiles are ejected from the comet through sunlight. The ejected molecules are then broken up through a process of photoionization, where ultraviolet light strikes the molecules, causing them to break apart. It is these ionized molecules that we observe as the coma and tail of a comet.

But we now know that reactions in space can be much more complex and subtle. In this case, we now know that free electrons play a role in the breakup of ejected molecules. The work was recently published in Astronomy & Astrophysics, and details the role of electrons in the chemistry of cometary atmospheres. The data for this research came from the Rosetta probe orbiting Comet 67P/Churyumov-Gerasimenko. Using ultraviolet spectroscopy, the team found that rather than ionizing various molecules directly, the ultraviolet light liberates electrons from water molecules in the coma. These electrons then interact with other molecules to break them apart.

It’s a rather surprising result, but it’s also a great example of how better data allows us to refine a simple model into a more subtle and accurate one.

Paper: P.D. Feldman, et al. Measurements of the near-nucleus coma of comet 67P/Churyumov-Gerasimenko with the Alice far-ultraviolet spectrograph on Rosetta. A&A DOI: 10.1051/0004-6361/201525925 (2015)

The post Electric Avenue appeared first on One Universe at a Time.

Crowdsourcing can be a great tool for astronomers, particularly when data needs to be gathered or analyzed by hand. One of the challenges of crowdsourcing is ensuring that the results are valid. Crowdsourcers are volunteers, and aren’t generally trained astronomers. While it might seem like the results would be of low quality because of that, we’ve actually found the results to be quite good. You have to be careful of data bias, but that’s true for any research. You can even used crowdsourced data without without trained volunteers, as a recent work in the Astronomical Journal has shown.

Solid lines show statistical orbits matched to the images. The dotted line shows the JPL calculated orbit.

The authors wanted to make an accurate determination of the orbit of a comet known as 17P/Holmes. Rather than relying upon volunteers, the authors did a Yahoo! image search for amateur photographs of the comet. They easily found thousands of images of varying quality, and narrowed them down to 1,299 comet Holmes images where background stars could be seen. Of these, 422 had time stamps contained within the image. The background stars in these photographs were then used to determine the apparent location of Holmes for each image. From this the authors created a statistical sampling of the movement of Holmes through the sky. They then fit this data to derive a calculated orbit of the comet. Their result was in good agreement with the JPL ephemeris, which is the “official” measured orbit of the comet.

What’s amazing about this result is that none of these images were intended as orbit data. Amateur images are often done for their visual appeal. They can be manipulated for effect. Scientific data like the location and time of gathering aren’t usually recorded. Despite this, the resulting data was really good. Taken as a collective whole, the results were certainly good enough to produce accurate results. This could be particularly useful for unexpected events such as meteors or close supernovae.

Paper: Dustin Lang and David W. Hogg.  Searching for comets on the World Wide Web: The orbit of 17P/Holmes from the behavior of photographers. The Astronomical Journal 144 46 (2015)

The post A Bunch of Yahoos appeared first on One Universe at a Time.

This week the research journal Science published a special issue on the initial results of the Rosetta/Philae mission. Along with it came several high-resolution and color images of the comet 67P Churyumov-Gerasimenko. The images alone are pretty astounding. The surface is diverse, with evidence of fracturing, faint jets, and a mottling of colors. It is clearly a complex and dynamic body. While the images are appealing, other data is telling a fascinating story.  One of these stories concerns the formation of the comet’s magnetosphere. 

A color image of 67P’s surface. Credit: ESA/Rosetta/NAVCAM

Comets like 67P don’t have a strong intrinsic magnetic field, so by themselves they don’t have a magnetosphere to protect themselves against solar wind. It’s icy surface is therefore bombarded by ions and magnetic fields. But as the comet approaches the Sun, volatiles such as water sublime to produce a thin atmosphere. Some of the water vapor is then ionized by ultraviolet sunlight, and these ions interact with the magnetic fields of interplanetary space. As the atmosphere of the comet gets thicker, and more of it is ionized it becomes conductive. The solar wind accelerates some of the atmospheric ions at high speed, and the resulting current induces a magnetic field around the comet. Eventually the magnetic field is strong enough that it pushes back against the solar wind, creating a magnetosphere.

At least that’s what we’ve thought. Previous fly-bys of comets such as Halley have found that comets don’t have strong intrinsic magnetic fields, and we’ve seen more active comets affect the surrounding magnetic environment. But now results from Rosetta have confirmed this model by directly observing it happen.

The team observed both neutral and ionized water in the comets atmosphere, as well as the magnetic fields in the region. They collected data as the comet was more than 3.6 AU to when it made its closest approach to the Sun at about 1.25 AU. They found an initial faint atmosphere penetrated by the solar wind, then watched as the atmosphere thickened to the point where it started resisting the wind through an induced magnetosphere. They also found the atmosphere is unevenly distributed about the comet (as different surface regions produced more or less volatiles) and that even a faint atmosphere interacts more strongly with the solar wind than initially supposed.

This is why missions like Rosetta are important. Observing the complex interaction of solar wind and cometary atmosphere can only be done on site. It doesn’t show up in images. So enjoy the flood of new color comet pictures, but remember that we can’t see the colors of the wind.

Paper: Hans Nilsson, et al. Birth of a comet magnetosphere: A spring of water ions. Science, Vol. 347 no. 6220 (2015)

The post Colors of the Wind appeared first on One Universe at a Time.

Comet Lovejoy is still visible in the night sky, so if you get a chance you should check it out.  If you have seen it, you might have noticed a distinctly green color to it. That isn’t an optical illusion, because Lovejoy is really green.

Structure of a comet. Credit: NMM London

Usually when you observe a comet directly, it will appear white, or slightly bluish. The white is due to sunlight reflecting off the dusty tail of the comet, and the blue is from the gas tail of the comet. Photographs can typically reveal these colors in rich detail, compared to the limited color perception of our eyes. But sometimes the gas emitted can have a greenish hue. Many comets have an abundance of compounds such as cyanide (CN₂) and carbon (C₂). When ionized these compounds emit light in the green spectrum. The light they emit is much brighter than things like hydrogen (even though hydrogen is more common), and that combined with our sensitivity to green light means that a comet can appear green.

Green comets are fairly common, but make for a rare color in the night sky since there are no green stars.

The post Easy Being Green appeared first on One Universe at a Time.