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Debris Disks: Searching for Dust to Find Planets


A star system where gas and dust have formed into a disk around a newly formed star. The leftover disk will most likely form planets, comets and asteroids. Credit: NASA

No one is ever excited when the topic of “dust” is brought up. Usually dust is a hindrance – something you sweep away during spring-cleaning, or an annoyance because your allergies can’t handle it. But for astronomers, finding dust around another star – i.e., circumstellar dust – is like finding the next piece of an interstellar puzzle. That’s because circumstellar dust holds clues to understanding not only the origins of planets outside of our solar system, but also gives us a leg up in figuring out our place in the Universe. (more…)

The bright barchan

ESP_039568_1120_0.794xA piece of Mars: Most dunes on Mars are dark, like these and these. So why is this one bright? It’s adjacent to a more typical, dark dune. It’s possible that there are two populations of sand here that are different enough in size or density, and so they respond to different winds – thus producing remarkably different dunes in the same location. (HiRISE ESP_039568_1120, NASA/JPL/Univ. of Arizona)

Sometimes I just have no idea

ESP_039595_1230_0.631xA piece of Mars: The smooth areas are eroded dunes, separated by fields of boulders (the scene is 1.51×1.14 km or 0.93×0.71 mi). The largest boulder near the center is 7.5 m (25 ft) across, the size of a small RV. The interesting wave patterns on the lower sides of the smooth dunes… well, I don’t know. My best guess is it’s another type of bedform created from the sand of the smooth dunes. Do you know? (HiRISE ESP_039595_1230, NASA/JPL/Univ. of Arizona)

Dunes ignoring small hills

ESP_039524_1445_1.0xA piece of Mars: What happens to dunes as they move over rough terrain? This is what a barchan looks like on a relatively flat surface. If the hills are smaller than the dune, then it does its best to pretend they don’t exist, like the one in this image. It’s 175m (574ft) wide and 190m (623ft) long, with a slipface indicating overall migration to the northeast. (HiRISE ESP_039524_1445, NASA/JPL/Univ. of Arizona)

On Mars, the wind wins

ESP_039057_1485_1.0x A piece of Mars: This scene (600×450 m or 1969×1476 ft) is covered in small craters, formed by the splash of a larger crater nearby. They cover everything, even the bright ripples visible on the right. So the ripples were there before the impact that formed all these little craters. And yet… there are itsy little gray ripples on the upper right, merging with the crater rims – these are new ripples, younger than the craters. On Mars, it’s the wind that wins in the end. (HiRISE ESP_039057_1485, NASA/JPL/Univ. of Arizona)

Wind eroded mantle

ESP_039195_1755_0.398xA piece of Mars: The curving ridge of a mountain has signs of many small landslides. Mantled on top of these is an older set of landslides that has been partially eroded away. The rippled edge of this older deposit suggests that it is wind that has done the erosion. So the history here goes: mountains, then landslides, then wind erosion, then new smaller landslides. (HiRISE ESP_039195_1755 NASA/JPL/Univ. of Arizona)

Bearded craters and dunes

A piece of Mars: This 600×450 m (1969×1476 ft) scene has a complex sedimentary history. How are bearded craters and dunes formed? They weren’t always bearded. At some point, a deposit of bright material accumulated on this surface, and was then eroded so that all that remains of it is what is protected by topography (anything that pokes up like dunes or crater rims). Can you find the boulder that has tumbled downslope (it too has a beard!). (HiRISE ESP_038826_1700, NASA/JPL/Univ. of Arizona)

Hello from AAS!

Happy new year, Internet! I’m starting off the year at the 225th meeting of the American Astronomical Society. It’s an annual conference where all the professional astronomers in the United States get together and talk about space! There’s been some really cool presentations, including the discovery of Earth-sized planets in possibly habitable orbits around other stars by Kepler. Sounds pretty cool right?

A subset of the GPI team was here for the AAS. We gave an update on the GPI Exoplanet Survey, presented posters on debris disks and exoplanets imaged by GPI, and even had a press conference on recent GPI results!

In addition to all the GPI results, the GPI team also had a team lunch to talk about starlight subtraction. Even with the star masked out, starlight still diffracts around the coronagraph and hides the faint exoplanets and debris disks that we are trying to see. As you might guess, starlight subtraction is a really important for GPI, especially with the kickoff of the GPI Exoplanet Survey just a couple of months ago. The content of meeting was a bit technical so I’ll spare you the summary here. It was a productive lunch though, and overall it’s been a great conference!

The only good picture is the one in which my eyes are closed.

The GPI Team in Seattle. Photo credit: Marshall Perrin

The Gemini Planet Imager Produces Stunning Observations In Its First Year


GPI imaging of the planetary system HR 8799 in K band, showing 3 of the 4 planets. (Planet b is outside the field of view shown here, off to the left.) These data were obtained on November 17, 2013 during the first week of operation of GPI and in relatively challenging weather conditions, but with GPI’s advanced adaptive optics system and coronagraph the planets can still be clearly seen and their spectra measured (see Figure 2). Image Credit: Christian Marois (NRC Canada), Patrick Ingraham (Stanford University) and the GPI Team.

Gemini Observatory
Media Advisory

For release at the American Astronomical Society meeting press confer-ence January 6, 2015, 10:15am (PST)

Publication-quality images available at:


Stunning exoplanet images and spectra from the first year of science operations with the Gemini Planet Imager (GPI) were featured today in a press conference at the 225th meeting of the American Astronomical Society (AAS) in Seattle, Washington. The Gemini Planet Imager GPI is an advanced instrument designed to observe the environments close to bright stars to detect and study Jupiter-like exoplanets (planets around other stars) and see proto-stellar material (disk, rings) that might be lurking next to the star.


Happy New Year to the Planet!

I decided to do something new to start the New Year. I translated a podcast from a program called Geopolitics on France Inter written by Anthony Bellanger. You can listen to the original French version here.

I like the text since it is quite optimistic and it summarizes the progresses that we have made over the past 50 years. The world is not perfect yet, but it is indeed a better place.


Are there any reasons to wish people a Happy New Year 2015?

I believe there are many and would like to explain why.

First: our health. Never have so many people all over the world been so healthy and well cared for.

It may seem strange to say that when nearly 8,000 people have died of Ebola in West Africa in recent months, and when the epidemic is far from defeated—yet it’s true.

Over the last half century , the infant mortality rate has fallen by two-thirds and the average human lifespan has increased by twenty years and continues to grow. Better yet, the difference in life expectancy between rich and poor countries is narrowing year by year.

Thanks to modern medicine, diseases that decimated entire populations throughout history are almost eradicated. The number of polio cases, for example, has fallen by 99% since 1988.

Between 2000 and 2015, the number of global malaria cases has dropped in half thanks to a global mobilization against the disease. Even AIDS, which appeared only 30 years ago, is now tested for and treated all over the world.

What about hunger and education?

Here, too, things are looking up. Hunger around the world declines annually. Since the early 90s — only 25 ago! — the percentage of undernourished people around the world has fallen by half.

The great famines that killed tens of thousands of people in the 1980s — in Ethiopia, for example —have disappeared. The world is better organized than ever and extremely efficient at delivering emergency medical and food aid when and where it is needed.

On the education front, results are even more impressive: In only 10 years, school enrollment for boys and girls has increased from 84 to 89% in primary grades and 60 to 73% in secondary grades. Around the world, three out of four children go to school until they are at least 14 years old!

We see similar improvements in the area of extreme poverty, which has fallen by 50 percent since 1990. This is unheard of in human history.

What is the source of this improvement?

We all are! Despite what we may hear or say, international institutions — the UN, NGOs and many others —work effectively: they treat, train, vaccinate, feed and intervene anywhere in the world where they are needed.

Even freedom is rising: in the last half century, the number of democratic states has tripled, and half the world’s population now lives under this type of government which — though often imperfect — is a unique achievement in human history.

So yes, one may wish people a Happy New Year, knowing that there will be wars, massacres, and many other disasters but also knowing that we have never been better educated, cared for and nurtured than we are in 2015.