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AAVSO Exoplanet Archive for Amateur Astronomers

by Paul Gilster | Nov 19, 2018 | Exoplanetary Science | 13 Comments

Even today, I can well understand the reaction that Dennis Conti had when confronted with the prospect of finding a planet around another star with nothing more than an amateur instrument. Conti, who founded and now chairs the Exoplanet Section of the American Association of Variable Star Observers, was a newcomer to the transit method just a few years ago. "I thought, there's no way for someone with a backyard telescope to detect a planet going around a distant star," he says, looking back from the vantage of one now immersed in such observations. My boyhood 3-inch reflector was not a backyard instrument -- too many trees back there. So it became a front-yard telescope. Absent the technological innovations of the past five decades, I could only imagine vast instruments for studying objects around other stars. The transit method in exoplanet detection was a long way off, but the idea of seeing not a planet itself but a change in starlight as the planet crossed the face of its host...

Crater Beneath the Greenland Ice

by Paul Gilster | Nov 16, 2018 | Asteroid and Comet Deflection | 41 Comments

A crater roughly the size of the area inside Washington DC's beltway has been found beneath the Greenland ice. On this, some thoughts, but first, a reminiscence. If you've ever driven the Capital Beltway at rush hour, you'll have some sense of the crater's size. My own experiences of it have been few, but the most memorable was the afternoon I spent at NASA Goddard Space Flight Center, where Greg Benford was speaking. We had agreed that after his talk, Greg and I would head out for dinner at a local restaurant, the exact venue to be determined later. It was about 5:00 PM when we were in the GSFC parking lot ready to go, now joined by Gloria Lubkin, editor emerita at Physics Today. With the help of Greg's nephew Dominic, we had chosen a French restaurant about 10 miles away. The problem: Greg and Gloria were in one car, I was in another, and it was rush hour. An out-of-towner who rarely got to DC, I was not remotely prepared for the beltway under these conditions. I had no smartphone...

Spitzer Size Constraints on ‘Oumuamua

by Paul Gilster | Nov 15, 2018 | Deep Sky Astronomy & Telescopes | 65 Comments

The first interstellar object detected in our own Solar System, 'Oumuamua has a pleasing name, translating from the Hawaiian as something like 'far visitor first to arrive,' or words to that effect. It's also proven a frustrating catch ever since detected by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii during a search for near-Earth asteroids. We've put telescope resources on Earth and in space on the object, but our observing time is up. For 'Oumuamua is now well on its way out of the Solar System, so we're left to massage the data we have in hopes of gaining new insights. Davide Farnocchia (Center for Near Earth Object Studies, JPL) encapsulates the issue: "Usually, if we get a measurement from a comet that's kind of weird, we go back and measure it again until we understand what we're seeing. But this one is gone forever; we probably know as much about it as we're ever going to know." Thus Avi Loeb's recent paper with Shmuel Bialy discussing the object's...

A Super-Earth Orbiting Barnard’s Star

by Paul Gilster | Nov 14, 2018 | Exoplanetary Science | 64 Comments

The detection of a planet around Barnard’s Star really hits home for me. No, this isn’t a habitable world, but the whole topic of planets around this star has resonance for those of us who remember the earliest days of exoplanet study, which could be extended back to Peter van de Kamp’s work at Swarthmore’s Sproul Observatory in Pennsylvania. The astronomer thought he had found evidence for a 1.6 Jupiter mass planet in a 4.4 AU orbit there, based on what he interpreted as telltale wobbles in photographic plates of the star taken between 1916 and 1962. This work, ending in the early 1970s, turned out to be the result of errors in the instrument van de Kamp was using, but the buzz about possible planets around Barnard’s Star had been sufficient to create a small crest of enthusiasm for exoplanet studies in general. The British Interplanetary Society saw in Barnard’s Star a target worth investigating, and designed their Daedalus star probe around a mission there. In any case, van de...

Low Metallicity in Compact Multi-Planet Systems

by Paul Gilster | Nov 13, 2018 | Exoplanetary Science | 21 Comments

When astronomers talk about metals, they're using the term in a specific sense. A metal in stellar terms is any element heavier than helium. Thus iron, silicon, magnesium and carbon qualify, all elements that are components of small, rocky planets. It was iron that John Michael Brewer (Yale University), Debra Fischer and colleagues singled out as a proxy in their recent work on the metal content of exoplanet systems. The work focuses specifically on compact, multi-planet systems as one of several system architectures found in close orbit of a host star. What's interesting here is that these domains seem mutually exclusive, or almost so. Unlike our Solar System, a system with multiple planets on tight orbits can squeeze its worlds into a region as close as Mercury. Likewise near the host star, we sometimes find massive planets in close orbits, known as 'hot Jupiters.' Few of these have close planetary neighbors, and few compact multi-planet systems have massive planets. And there is...

Lucy in the Sky

by Paul Gilster | Nov 12, 2018 | Outer Solar System | 12 Comments

Extended operations at multiple targets, as Dawn showed us, are possible with ion propulsion. But we still learn much from flybys, something New Horizons reminded us with its spectacular success at Pluto/Charon, and again reminds us as it closes on MU69. Likewise, a mission called Lucy will visit multiple objects, using traditional chemical propulsion with gravity assist to achieve flybys of seven different targets. The destination: Jupiter's trojan asteroids. With launch scheduled for 2021, Lucy's will study six Jupiter trojans and one asteroid in the Main Belt. Image: Jupiter's extensive trojan asteroids, divided into 'Trojans' and 'Greeks' in a nod to Homer, but all trojans nonetheless. Credit: "InnerSolarSystem-en" by Mdf at English Wikipedia - Transferred from en.wikipedia to Commons. Licensed under Public Domain via Commons. The trojans are interesting bodies orbiting at the L4 and L5 Lagrange points 60° ahead and behind the gas giant. Jupiter's trojans are the best known...

Parker Solar Probe: Already a Record Setter

by Paul Gilster | Nov 9, 2018 | Missions | 27 Comments

Over the sound system in the grocery store yesterday, a local radio station was recapping events of the day as I shopped. The newsreader came to an item about the Parker Solar Probe, then misread the text and came out with "The probe skimmed just 15 miles from the Sun's surface." Yipes! I was in the vegetable section but you could hear him all over the store, so I glanced around to see how people had reacted. Nobody as much as raised an eyebrow, which either says people tune out background noise as they shop or they have little knowledge of our star. The correct number is 15 million miles (24,1 million kilometers), and it's still a hugely impressive feat, but I hope the station got the story right later on. I go easy on this kind of thing because it's easy enough to make a mistake when reading radio copy (I've done this myself). Anyway, there is always some listener who calls it in, which I should have but didn't. I was pushed for time that morning, making choices about squash and...

Fine-Tuning Mechanisms for Water Delivery

by Paul Gilster | Nov 8, 2018 | Exoplanetary Science | 19 Comments

We’ve long been interested in how the Earth got its oceans, with possible purveyors being comets and asteroids. The idea trades on the numerous impacts that occurred particularly during the Late Heavy Bombardment some 4.1 to 3.8 billion years ago. Tuning up our understanding of water delivery is important not only for our view of our planet’s development but for its implications in exoplanet systems with a variety of different initial conditions. Image: This view of Earth’s horizon was taken by an Expedition 7 crewmember onboard the International Space Station, using a wide-angle lens while the Station was over the Pacific Ocean. Credit: NASA. But the picture becomes more complex when we compare regular hydrogen atoms (one proton, one electron) with ‘heavy hydrogen,’ or deuterium atoms. The latter have a neutron in addition to a proton in the nucleus. A recent paper in the Journal of Geophysical Research digs into isotope ratios, the ratio of deuterium to ordinary hydrogen atoms,...

On the Earliest Stars

by Paul Gilster | Nov 7, 2018 | Deep Sky Astronomy & Telescopes | 30 Comments

If you’ve given some thought to the Fermi question lately -- and reading Milan ?irkovi?’s The Great Silence, I’ve been thinking about it quite a bit -- then today’s story about an ancient star is of particular note. Fermi, you’ll recall, famously wanted to know why we didn’t see other civilizations, given the apparent potential for our galaxy to produce life elsewhere. Now a paper in The Astrophysical Journal adds punch to the question by making the case that the part of the galaxy in which we reside may be older than we have thought. Finding that our Sun is younger than many nearby stars, an issue that Charles Lineweaver (Australian National University), among others, has examined, would allow even more time for civilizations to have emerged in the galactic neighborhood. But let’s now leave Fermi behind to look at the tiny star that prompts these ruminations (and to be sure, the paper on this star makes no mention of Fermi, but does tell us something quite interesting about the...

SETI in the Infrared

by Paul Gilster | Nov 6, 2018 | Astrobiology and SETI | 60 Comments

One of the problems with optical SETI is interstellar extinction, the absorption and scattering of electromagnetic radiation. Extinction can play havoc with astronomical observations coping with gas and dust between the stars. The NIROSETI project (Near-Infrared Optical SETI) run by Shelley Wright (UC-San Diego) and team is a way around this problem. The NIROSETI instrument works at near-infrared wavelengths (1000 - 3500 nm), where extinction is far less of a problem. Consider infrared a 'window' through dust that would otherwise obscure the view, an advantage of particular interest for studies in the galactic plane. Would an extraterrestrial civilization hoping to communicate with us choose infrared as the wavelength of choice? We can't know, but considering its advantages, NIROSETI's instrument, mounted on the Nickel 1-m telescope at Lick Observatory, is helping us gain coverage in this otherwise neglected (for SETI purposes) band. I had the chance to talk to Dr. Wright at one of...

Bennu Coming into Focus

by Paul Gilster | Nov 5, 2018 | Asteroid and Comet Deflection | 16 Comments

Following a week when we learned of the end of both Kepler and Dawn, let's turn to a mission that is just coming into its own. The earliest images of target asteroid 101955 Bennu from OSIRIS-REx have been tightened by computer algorithm to heighten their resolution. The mission plan here is to examine the small object (approximately 500 meters in mean diameter) and return samples to Earth in 2023. More than a few people have reacted to the similarity in shape between this asteroid, a carbonaceous (C-type) Earth-crossing object in the Apollo group of near-Earth asteroids, and 162173 Ryugu, now under active exploration by the Japanese Hayabusa2 mission. Here we're looking at Bennu through the OSIRIS-REx PolyCam, one of three cameras aboard the spacecraft, from a distance of 330 kilometers. The image is a combination of eight images taken by PolyCam that have been combined to cancel out the asteroid's rotation and produce a high-resolution result. Of the comparison to Ryugu, Julia de...

Farewell to Dawn

by Paul Gilster | Nov 2, 2018 | Outer Solar System | 19 Comments

It seems to be a week for endings. Following the retirement of the wildly successful Kepler spacecraft, we now say goodbye to Dawn following an extraordinary eleven years that took us not only to orbital operations around Vesta but then on to detailed exploration of Ceres. The spacecraft ran out of hydrazine, with the signal being lost by the Deep Space Network during a tracking pass on Wednesday. No hydrazine means no spacecraft pointing, vital in keeping Dawn's antenna properly trained on a distant Earth. I immediately checked to see if mission director and chief engineer Marc Rayman had gotten off a post on his Dawn Journal site, but he really hasn't had time to yet. It will be interesting to see what Dr. Rayman says, and it's appropriate here to thank him for the continuing updates and insights he provided throughout the Dawn mission. Keeping space exploration in front of the public is essential for continuing funding of deep space robotic missions, as both the Dawn and New...

The Stripes of Dione

by Paul Gilster | Nov 1, 2018 | Uncategorized | 8 Comments

Usually when we talk about outer planet moons with oceans, we're looking at Jupiter's Europa, and Saturn's Enceladus. But evidence continues to mount for oceans elsewhere. In the Jupiter system alone, Callisto and Ganymede are likewise strong candidates, while Saturn's Titan probably has a layer of liquid water. Pluto's moon Charon may possess an ocean of water and ammonia, to judge from what appears to be cryovolcanic activity there. At Neptune, Triton's high-inclination orbit should produce plenty of tidal heating that may support a subsurface ocean. Let's pause, though, on another of Saturn's moons, Dione. Here we have evidence from Cassini that this world, some 1120 kilometers in diameter and composed largely of water ice, has a dense core with an internal liquid water ocean, joining Enceladus in that interesting system. But what engages us this morning is not liquid water but a set of straight, bright stripes discovered on the surface and discussed in a new paper from Alex...

Thoughts on the End of the Kepler Mission

by Paul Gilster | Oct 31, 2018 | Exoplanetary Science | 24 Comments

The Kepler spacecraft has been with us long enough (it launched in 2009) and has revealed so much about the stars in our galaxy that its retirement -- Kepler lacks the fuel for further science operations -- is cause for reflection. The end of great missions always gives us pause as we consider their goals and their accomplishments, and offer up our gratitude to the many people who made the mission happen. Let's try to back up and see things in their totality. Image: An artist's conception of Kepler at work. Credit: NASA/Ames/Dan Rutter. Kepler's job was essentially statistical, an attempt to look at as many stars as possible in a particular field of stars, so that we could gain insights into the distribution of planets there, and thus deduce something about likely conditions galaxy-wide. We didn't know in 2009 that there was statistically at least one planet around every star, nor did we know just how diverse the worlds Kepler found, more than 2,600 of them, would be. Moreover,...

‘Oumuamua, Thin Films and Lightsails

by Paul Gilster | Oct 29, 2018 | Outer Solar System | 192 Comments

The interstellar object called ‘Oumuamua continues to inspire analysis and speculation. And no wonder. We had limited time to observe it and were unable to obtain a resolved image to find out exactly what it looks like. This morning I want to go through a new paper from Shmuel Bialy and Abraham Loeb (Harvard University) considering the role radiation pressure from the Sun could play on this deep sky wanderer. Let’s also review what we do know about it, which I’ll do with reference to this paper’s introduction, where recent work is discussed. For it seems that each time we look at ‘Oumuamua anew, we find something else to talk about. Discovered in October of 2017 by the Pan-STARRS survey (Panoramic Survey Telescope and Rapid Response System) in Hawaii, ‘Oumuamua stood out because of its hyperbolic trajectory, flagging it as an interstellar object, the first ever discovered passing through the Solar System. The object’s lightcurve indicated both that it was tumbling and had an aspect...

Hayabusa2 Team Looks Toward Sample Collection

by Paul Gilster | Oct 26, 2018 | Asteroid and Comet Deflection | 13 Comments

With two rovers and a lander already deployed on the asteroid 162173 Ryugu, the Japan Aerospace Exploration Agency (JAXA) must be basking in the glow of an unusually successful venture. Now we turn to a key part of the Hayabusa2 mission, the retrieval of a surface sample. Two touchdown rehearsals have gone well, providing detailed views of the asteroid's surface. The plan is to return samples to Earth in December of 2020, but let's continue to take one thing at a time. Sample retrieval can be dicey, as we saw with the first Hayabusa. Once known as MUSES-C, the original Hayabusa reached asteroid Itokawa in September of 2005 (I can't believe it was that long ago -- as the cliché would have it, it seems like yesterday). A series of enroute problems included a solar flare that damaged the craft's solar cells and the failure of attitude-adjusting reaction wheels, while the launch of a probe called MINERVA also failed. Nonetheless, surface particles from Itokawa were successfully...

Game-Changer: A Pluto Orbiter and Beyond

by Paul Gilster | Oct 25, 2018 | Outer Solar System | 30 Comments

To say that the Space Science and Engineering Division at Southwest Research Institute has been busy of late is quite an understatement. Alan Stern, principal investigator for New Horizons, has been leading an SwRI study examining just how we might operate an orbiter at Pluto/Charon, with results that are surprising and encouraging for the future of such a project. Working with spaceflight engineer and mission designer Mark Tapley and planetary scientist Amanda Zangari, as well as project manager John Scherrer and software lead Tiffany Finley, Stern has been looking at an orbital tour of Pluto built around a series of gravity assist maneuvers involving Charon, its large moon. The mission would use the kind of electric propulsion system we saw in the Dawn mission to Vesta and Ceres, and by clever use of gravity assists, would pull off another Dawn feat by leaving Pluto once its orbital operations were concluded and moving into the Kuiper Belt for encounters with further objects....

A Thermal Map of Europa (& an Intriguing Anomaly)

by Paul Gilster | Oct 24, 2018 | Outer Solar System | 14 Comments

Europa stays in this news this morning as we continue to correlate recent observations with the invaluable results of the Galileo mission. Hubble data have played a role in this, with researchers identifying plume activity in 2013 that recalled the geysers of Enceladus, a possible indication of venting from the subsurface ocean. But analysis of Cassini data from its 2001 Jupiter flyby enroute to Saturn showed no evidence of plume activity through its ultraviolet imaging spectrograph (UVIS). So what exactly did Hubble see? Yesterday's post highlighted Julie Rathbun's contention that if they are there, Europan plumes show no thermal signature in Galileo data, while Xianzhe Jia (University of Michigan) and the SETI Institute's Melissa McGrath have used Galileo magnetometer data to support possible plume activity. We may need Europa Clipper to resolve the matter. Now the 66 dish antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) have been turned on Europa in an attempt...

No Heat Signature of Europan ‘Plumes’

by Paul Gilster | Oct 23, 2018 | Outer Solar System | 36 Comments

One of the youngest surface features on Europa draws attention because of its possible connection with what lies beneath the Jovian moon's ice. The dark center of Pwyll crater, visible in the image below, is some 40 kilometers across, with a central peak reaching about 600 meters. At issue is the terrain resulting from the impact causing the crater. An impact perhaps 20 million years ago seems to have blown water and ice across the Europan surface. Evidence of a possible plume from Europa's ocean in this area is the subject of continuing work. The bright terrain around the crater suggests water ice, and note, too that the Pwyll impact left ejecta rays as far as the Conamara Chaos region 1000 kilometers to its north. Conamara Chaos features themselves have been studied extensively for terrain suggestive of melting and refreezing ice. We saw recently how Xianzhe Jia (University of Michigan), working with the SETI Institute's Melissa McGrath, used data from the Galileo mission to...

Birth of a Supercluster

by Paul Gilster | Oct 22, 2018 | Deep Sky Astronomy & Telescopes | 18 Comments

Long-time Centauri Dreams readers know that I love things that challenge our sense of scale, the kind of comparison that, for example, tells us that if we traveled the distance from the Earth to the Sun, we would have to repeat that distance 268,770 times just to reach the nearest star. It’s much simpler, of course, to say that Proxima Centauri is 4.25 light years from us, but it’s the relating of distances to things that are closer to us that gets across scale, especially for those who are just beginning their astronomical explorations. And I have to admit that the scales involved in going interstellar still pull me up short at times when I ponder them. So how about this for scale: We have somewhere between 200 billion and 300 billion stars in our galaxy (the number is flexible enough that you’ll see a wide range in the literature). Relate that to the Local Group, the gathering of galaxies that includes both the Milky Way and M31, the Andromeda Galaxy. These are the two most massive...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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