dust – A Darker View

Scientists Accurately Quantify Dust Around Planets in Search for Life

A new study from the Keck Interferometer, a former NASA project that combined the power of the twin W. M. Keck Observatory telescopes atop Mauna Kea, Hawaii, has brought exciting news to planet hunters. After surveying nearly 50 stars from 2008 to 2011, scientists have been able to determine with remarkable precision how much dust is around distant stars – a big step closer into finding planets than might harbor life. The discovery is being published in the Astrophysical Journal online, on December 8th.

A dusty planetary system (left) is compared to another system with little dust in this artist's conception. Credit NASA/JPL-Caltech — A dusty planetary system (left) is compared to another system with little dust in this artist’s conception. Credit NASA/JPL-Caltech

“This was really a mathematical tour de force,” said Peter Wizinowich, Interferometer Project Manager for Keck Observatory. “This team did something that we seldom see in terms of using all the available statistical techniques to evaluate the combined data set. They were able to dramatically reduce all the error bars, by a factor of 10, to really understand the amount of dust around these systems.”

The Keck Interferometer was built to seek out this dust, and to ultimately help select targets for future NASA Earth-like planet-finding missions.

Like planets, dust near a star is hard to see. Interferometry is a high-resolution imaging technique that can be used to block out a star’s light, making the region easier to observe. Light waves from the precise location of a star, collected separately by the twin 10-meter Keck Observatory telescopes, are combined and canceled out in a process called nulling.

“If you don’t turn off the star, you are blinded and can’t see dust or planets,” said co-author Rafael Millan-Gabet of NASA’s exoplanet Science Institute at the California Institute of Technology in Pasadena, California, who led the Keck Interferometer’s science operations system.

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Dusty Road

Rush hour for Mauna Kea is just before sunset. This is when the day crews are coming down, while the summit tours and telescope operators are heading up.

The timing of this rush can be variable depending on time of year and what time sunset occurs. Twice a year this rush is at its worst, when everyone heads up and down at the same time. This can lead to some difficult driving conditions… A lot of vehicles on a road that can be challenging. A cloud of fine cinder dust and a setting Sun just adding to the confusion…

Dust Out — Fine cinder dust creating a hazardous “dust out” condition on the Mauna Kea summit access road

Zodiacal Light

A strange glow visible long after sunset, or well before dawn, along the path of the Sun in the sky. Called the “False Dawn” by Muhammad in Islamic texts and by other classical sources, this glow is often confused with the light of dawn, or simply overlooked by many.

Once thought to be the extended atmosphere of the Sun, the zodiacal light was recognized as something interesting by early scientists. The real reason for the glow was not understood until described by Nicolas Fatio de Duillier in 1684.

The answer is simply dust.

Space is not only very big and mostly empty, it can also be dirty. Dust from comets, dust from asteroid collisions, dust floating in orbit about the Sun, reflecting sunlight and glowing across the sky. Because this dust lies in the plane of the solar system the glow is visible as a band along the ecliptic and through the constellations of the zodiac. The dust is thickest, and the glow brightest nearer the Sun, thus the glowing dust is best seen when the Sun is just out of sight, after dusk, or before dawn. The light is simply reflected light. Looking at the spectrum of the zodiacal light shows it to be sunlight, with the same spectral features.

The zodiacal light can be quite bright, clearly visible to any who look in the hour after dusk, or before dawn. It can be bright enough to be a nuisance to amateur astronomers attempting to view through their telescopes. At the same time it is a sign of clear dark skies, as it is otherwise hidden by the glow of artificial light. The slightest amount of moonlight or light pollution and this glow disappears from sight.

The effect can be seen completely across the sky, along the ecliptic, as a very faint glowing band when viewed from the darkest of places. Directly opposite the Sun in the sky is a brighter spot in the glow, the gegenschein or counterglow. A form of glory, the dust reflects sunlight back in the direction it came.

The zodiacal band and the gegenschein are both visible from Mauna Kea on a dark night. From this dark place the most subtle of astronomical spectacles can be appreciated.