Planet earth photographed by spacecraft

Planet earth photographed from space. Two Views of Home: These images show views of Earth and the moon from NASA's Cassini (left) and MESSENGER spacecraft (right) from July 19, 2013. (Credit: NASA/JPL-Caltech/Space Science Institute and NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

From ScienceDaily:

NASA Releases Images of Earth by Two Interplanetary Spacecraft

July 22, 2013 — Color and black-and-white images of Earth taken by two NASA interplanetary spacecraft on July 19 show our planet and its moon as bright beacons from millions of miles away in space.

NASA’s Cassini spacecraft captured the color images of Earth and the moon from its perch in the Saturn system nearly 900 million miles (1.5 billion kilometers) away. MESSENGER, the first probe to orbit Mercury, took a black-and-white image from a distance of 61 million miles (98 million kilometers) as part of a campaign to search for natural satellites of the planet.

In the Cassini images Earth and the moon appear as mere dots — Earth a pale blue and the moon a stark white, visible between Saturn’s rings. It was the first time Cassini’s highest-resolution camera captured Earth and its moon as two distinct objects.

It also marked the first time people on Earth had advance notice their planet’s portrait was being taken from interplanetary distances. NASA invited the public to celebrate by finding Saturn in their part of the sky, waving at the ringed planet and sharing pictures over the Internet. More than 20,000 people around the world participated.

“We can’t see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Linda Spilker, Cassini project scientist, at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini’s picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth.”

Pictures of Earth from the outer solar system are rare because from that distance, Earth appears very close to our sun. A camera’s sensitive detectors can be damaged by looking directly at the sun, just as a human being can damage his or her retina by doing the same. Cassini was able to take this image because the sun had temporarily moved behind Saturn from the spacecraft’s point of view and most of the light was blocked.

A wide-angle image of Earth will become part of a multi-image picture, or mosaic, of Saturn’s rings, which scientists are assembling. This image is not expected to be available for several weeks because of the time-consuming challenges involved in blending images taken in changing geometry and at vastly different light levels, with faint and extraordinarily bright targets side by side.

“It thrills me to no end that people all over the world took a break from their normal activities to go outside and celebrate the interplanetary salute between robot and maker that these images represent,” said Carolyn Porco, Cassini imaging team lead at the Space Science Institute in Boulder, Colo. “The whole event underscores for me our ‘coming of age’ as planetary explorers.”

In the MESSENGER image, Earth and the moon are less than a pixel, but appear very large because they are overexposed. Long exposures are required to capture as much light as possible from potentially dim objects. Consequently, bright objects in the field of view become saturated and appear artificially large.

“That images of our planet have been acquired on a single day from two distant solar system outposts reminds us of this nation’s stunning technical accomplishments in planetary exploration,” said MESSENGER Principal Investigator Sean Solomon of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y. “And because Mercury and Saturn are such different outcomes of planetary formation and evolution, these two images also highlight what is special about Earth. There’s no place like home.”

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL designed, developed and assembled the Cassini orbiter and its two onboard cameras. The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., designed and built MESSENGER, a spacecraft developed under NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the program for the agency’s Science Mission Directorate in Washington. JPL and APL manage their respective missions for NASA. The California Institute of Technology in Pasadena manages JPL for NASA.

More information about the picture and the Wave at Saturn campaign is available at:

To view the MESSENGER images, visit:

Smallest planet discovery

An artist's conception of the tiny new planet Kepler-37b, which is slightly larger than Earth's moon and orbits its host star every 13 days. Photo: NASA

From Nature:

A sub-Mercury-sized exoplanet

20 February 2013

Since the discovery of the first exoplanets, it has been known that other planetary systems can look quite unlike our own. Until fairly recently, we have been able to probe only the upper range of the planet size distribution, and, since last year, to detect planets that are the size of Earth or somewhat smaller. Hitherto, no planets have been found that are smaller than those we see in the Solar System.

Here we report a planet significantly smaller than Mercury. This tiny planet is the innermost of three that orbit the Sun-like host star, which we have designated Kepler-37. Owing to its extremely small size, similar to that of the Moon, and highly irradiated surface, the planet, Kepler-37b, is probably rocky with no atmosphere or water, similar to Mercury.

See also here. And here.

NASA's artist's illustration compares the planets in the Kepler-37 system to the moon and planets in the solar system. Photo: NASA

Ice on planet Mercury

From Nature:

Stores of ice confirmed on Sun-scorched Mercury

MESSENGER finds evidence of pure water ice near planet’s north pole.

29 November 2012
Water ice is abundant in Mercury's dark polar craters. Photo NASA/Johns Hopkins Uni Applied Phys Lab/Carnegie Inst of Washington

Talk about a land of fire and ice. The surface of Mercury is hot enough in some places to melt lead, but it is a winter wonderland at its poles — with perhaps a trillion tonnes of water ice trapped inside craters — enough to fill 20 billion Olympic skating rinks.

The ice — whose long-suspected presence1 has now been confirmed by NASA’s orbiting MESSENGER probe — seems to be much purer than ice inside similar craters on Earth’s Moon, suggesting that the closest planet to the Sun could be a better trap for icy materials delivered by comets and asteroids. Three papers detailing the findings are published today in Science2, 3, 4.

Despite Mercury’s blistering 400 °C temperatures, the floors of many of its polar craters are in permanent shadow, because the planet’s rotational axis is perpendicular to its orbital plane, so its poles never tip towards the star. Indeed, radar pinged to the planet from Earth in the past 20 years has revealed bright regions1 near the poles consistent with metres-thick slabs of pure water ice.

But “radar does not uniquely identify water ice,” says David Lawrence, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Sulphur, for example, could have produced a similar radar signature.

Now, three different lines of evidence back the water-ice interpretation. Infrared laser pulses fired at the planet by MESSENGER’s Mercury Laser Altimeter have revealed bright regions inside nine darkened craters near the planet’s north pole2. These bright regions, thought to be water ice, line up perfectly with ultra-cold spots that, according to a thermal model of the planet that takes into account Mercury’s topography, should never be warmer than –170 °C3.

A third team, using MESSENGER’s Neutron Spectrometer, has spotted the telltale signature of hydrogen — which they think is locked up in water ice — in those same regions4. “Not only is water the best explanation, we do not see any other explanation that can tie all the data together,” says Lawrence, lead author of the spectrometer study.

So where did the water come from? The bright icy spots identified by MESSENGER’s laser are surrounded by darker terrain which receives a bit more sunlight and heat. The neutron measurements suggest that this darker area is a layer of material about 10 centimetres thick that lies on top of more ice, insulating it.

Dark materials

This darker material around the bright spots may be made up of complex hydrocarbons expelled from comet or asteroid impacts, says David Paige, a planetary scientist at the University of California, Los Angeles, and first author of  the thermal-model paper3.

Paige and his colleagues suggest that when these icy bodies slam into Mercury, their components migrate over time — by repeatedly vaporizing and precipitating — to the cooler poles, where they get stuck in the frigid polar craters.

But even there, sunlight will sometimes hit parts of the craters’ interiors, vaporizing the water ice and leaving behind ‘lag deposits’ of hydrocarbons that gradually become thicker and darker as they are chemically altered by sunlight.

Small impacts should have buried the surface if the ice were a billion years old, and the MESSENGER researchers believe it might be much younger than that, perhaps 50 million years old.

“The ice deposits we are looking at are not ancient,” says Paige.



  1. Slade, M. A., Butler, B. J. & Muhleman, D. O. Science 258, 635–640 (1992).

    Show context

  2. Neumann, G. A. et al. Science (2012).Show context
  3. Paige, D. A. et al. Science (2012).Show context
  4. Lawrence, D. J. et al. Science (2012).Show context

Mysterious Mercury and Planetary Pareidolia: Photos here.