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Too steep for ripples

ESP_043085_1670_1.0x A piece of Mars: This 480×270 m (0.3×0.17 mi) area is a steep slope that plunges down to the upper left. A pile of dark sand, covered by brighter tan dust, clings to the hillside. Usually the martian wind blows sand into ripples, and you can see where it’s tried to do that here. But the steep slope triggers thin dark avalanches of dark sand that compete with the wind in shaping the sandy surface. (HiRISE ESP_043085_1670 NASA/JPL/Univ. of Arizona)

Windy windows

ESP_043086_1715_1.0x A Piece of Mars: This 0.96×0.54 km (0.6×0.33 mi) area shows ripples forming on a layer of dark gray material. In a few spots, the gray layer has been eroded away (probably by wind scour), revealing the lighter, tan-colored terrain below. Geologists call these exposures windows, because you can see through one layer to another that’s underneath. (HiRISE ESP_043086_1715 JPL/NASA/Univ. of Arizona)

Gemini Planet Imager Exoplanet Survey — One Year Into The Survey

Orbital motion of 51 Eri b detected between two H-band observations taken with the Gemini Planet Imager in December 2014 and September 2015. From this motion, and additional observations of the system, the team of astronomers confirmed that this point of light below the star is indeed a planet orbiting 51 Eri and not a brown dwarf passing along our line of sight. (credit: Christian Marois & the GPIES team)

Orbital motion of 51 Eri b detected between two H-band observations taken with the Gemini Planet Imager in December 2014 and September 2015. From this motion, and additional observations of the system, the team of astronomers confirmed that this point of light below the star is indeed a planet orbiting 51 Eri and not a brown dwarf passing along our line of sight. (credit: Christian Marois & the GPIES team)

Thursday, November 12 2015 – 9:00 am, PST

AAS/SETI Institute press release presented at the DPS 2015 at National Harbor, MD, USA

The Gemini Planet Imager Exoplanet Survey (GPIES) is an ambitious three-year study dedicated to imaging young Jupiters and debris disks around nearby stars using the GPI instrument installed on the Gemini South telescope in Chile. On November 12, at the 47th annual meeting of the AAS’s Division for Planetary Sciences in Washington DC, Franck Marchis, Chair of the Exoplanet Research Thrust of the SETI Institute and a scientist involved in the project since 2004, will report on the status of the survey, emphasizing some discoveries made in its first year. (more…)

Crochet ripples

ESP_042360_1755_1.0x A Piece of Mars: This 480×270 m (1575×886 ft) area shows a seemingly endless field of ripples. They’re big, about 50 m (164 ft) from crest to crest, and probably about 5 m (16 ft) high. Is there a knit or crochet pattern out there that looks like this? You could market it to some Mars aeolian scientists… (HiRISE ESP_042360_1755, NASA/JPL/Univ. of Arizona)

Very long ripples

ESP_043098_1650_1.0x A Piece of Mars: Most of the scene (0.96×0.54 km or 0.6×0.34 mi) is one long slope of a dune. The crest is the line in the top right; the ground below is in the bottom left. If you ever walk along a dune or beach, you’ll see small ripples that can reach up to about a meter in length. But the ripples on this dune extend from the crest to the ground – they’re more than half a kilometer (more than a third of a mile) long! (HiRISE ESP_043098_1650 NASA/JPL/Univ. of Arizona)

Thoughts on GPI

In a major breakthrough for exoplanet discovery and exploration, the Gemini Planet Imager (GPI) is proving to be one of most powerful and effective instruments ever invented for directly imaging planets in orbit around other stars.

An artistic conception of the Jupiter-like exoplanet, 51 Eri b, seen in the near-infrared light that shows the hot layers deep in its atmosphere glowing through clouds. Because of its young age, this young cousin of our own Jupiter is still hot and  carries information on the way it was formed 20 million years ago.  credits: Danielle Futselaar & Franck Marchis, SETI Institute

An artistic conception of the Jupiter-like exoplanet, 51 Eri b, seen in the near-infrared light that shows the hot layers deep in its atmosphere glowing through clouds. Because of its young age, this young cousin of our own Jupiter is still hot and carries information on the way it was formed 20 million years ago.
credits: Danielle Futselaar & Franck Marchis, SETI Institute

The behind-the-scenes story of this project sheds light on the complexities and challenges of designing and building a truly game-changing instrument. We started work more than thirteen years ago under the leadership of Bruce Macintosh and the auspices of the Center for Adaptive Optics. At that time, a number of scientists, most from California and Canada, met to discuss building a groundbreaking adaptive optics (AO) system powerful enough to confront — and overcome — the challenging of directly collecting photons from young Jupiter-like exoplanets. The discovery of 51 Eri b, which was announced last August, is the culmination of that effort. 

(more…)

A light touch

ESP_042691_2060_0.15x A Piece of Mars: This 3.2×1.8 km (2×1.1 mi) area shows terrain covered by bright dust. Dark stripes are areas where wind has lightly scoured the surface, revealing the dark material beneath. Faint bright lines criss-cross the surface – these are tracks left by dust devils. The dust devils disturb the surface but don’t lift up enough dust to reveal the darker surface underneath. (HiRISE ESP_042691_2060, NASA/JPL/Univ. of Arizona)

Our Predictions about Pluto: Getting it Right/Getting it Wrong

Family portrait of Pluto's four small moons

Family portrait of Pluto’s four small moons

Back in June, my research colleage Doug Hamilton and I put out a paper in Nature magazine about the four small moons of Pluto. The timing was not accidental. Although the paper was the culmination of years of work with the Hubble Telescope, we knew that a lot of our predictions would be tested barely a month later, when the New Horizons spacecraft passed Pluto. Making predictions that might be proven wrong is part of the fun, and also part of the danger, of scientific research.

As we all know, the flyby was a great success and we are now waiting, patiently, for the slow trickle of images and other data to come back from the spacecraft. Today, NASA has released the first “family portrait” of Pluto’s four small moons. As someone who has spent years studying these objects as nothing but faint dots, I find it is enormously gratifying to see them as resolved bodies, with shapes, colors and surface features.

So what did we get right? Well, based on years of studying how the brightness of each body varies, we were able to determine the rough shapes of the two larger moons, Nix and Hydra. On that point, we nailed it! Also, by making assumptions about how bright the surfaces are, we could make estimates of their sizes. We have learned that the moons are a bit brighter than we expected, and therefore a bit smaller, but overall our predictions have held up well.

…with one big exception–Kerberos. Our paper predicted that Kerberos would be big and dark, whereas the image clearly shows an object that is small and bright. What went wrong? Well, it all comes down to the moons’ masses—how much they would weigh if you could put them on a scale. The only way to determine the masses of these moons is to study how each one subtly alters the courses of the others. Based on years of precise measurements, our colleagues believed that they had weighed Kerberos, and its mass was surprisingly high–about a third that of Nix and Hydra. On the other hand, from our measurements, it only reflected about 5% as much sunlight. The only way to make an object that faint and that massive is to make it very very dark. That darkness, comparable to that of a charcoal briquette, is not out of line with other bodies in the outer Solar System, but it certainly made it different from its Plutonian siblings.

We know now that Kerberos is small and bright. If the mass determination is right, then Kerberos is absurdly dense–many times denser than lead. That seems unlikely. We therefore conclude that we probably had a broken scale. Because weighing the moons of Pluto is such a tough job, this is not out of the question. Now that we have new and more precise measurements of the orbits of the moons, I boldly predict that we will soon learn that the mass of Kerberos is much lower than we had previously thought.

One word of caution, however: my bold predictions don’t always turn out to be right.

Peas in a pod

ESP_042697_2055_0.5x A Piece of Mars: These “peas-in-a-pod” are dunes covered in long ripples (the scene is 960×480 m, or 0.6×0.3 mi). They’re a bit odd, surrounded by a rippled apron. It reminds me of melted-looking dunes that are common in high southern latitudes, but these are at 21.5ºN. Yet more Mars mysteries to solve… (HiRISE ESP_042697_2055 NASA/JPL/Univ. of Arizona).

Is it windblown or not?

ESP_041982_1535_0.5
A Piece of Mars: This scene is 0.96×0.54 km (0.60×0.34 mi) across. There’s an old river valley running across it. The walls of the valley have been eroded and there’s a washboard pattern with a wavelength of ~6m (20 ft). When I first saw this image I thought it was exposed, tilted layers, but a closer look reveals a much smaller (and younger) set of ripples that are similarly oriented and almost certainly formed by the wind. What do you think? (HiRISE ESP_041982_1535, NASA/JPL/Univ. of Arizona)