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Earth's nearest neighbours have turned into uninhabitable hellholes. Understanding their transformation will teach us which rocky exoplanets might be fit for life CLOSE to the sun lie a pair of sizzling coals. You could be forgiven for thinking these strange worlds were two circles of hell: Mercury, a black and blasted plain, and Venus, a sweltering world beset by rain of pure acid. But for all the terror of their outward appearance, their insides are remarkably familiar. Along with Earth and Mars, they form the solar system’s only rocky planets, a stark contrast to the bloated gas giants that make...

NEVER LOOK DIRECTLY AT THE SUN. SPECIAL GLASSES OR FILTER WILL BE NEEDED TO VIEW. Just like the solar eclipse in 2017, special glasses or filters will be required to view the transit. Since Mercury is so small, however, you will also need binoculars or a telescope to view. Use extreme caution when using magnification to look at the sun. If using binoculars or a telescope, make sure the proper solar film is installed on the front lens, not the eyepiece for safe viewing. An even safer way to view the sun is to project the image on to something.

Explanation: On May 9, innermost planet Mercury crossed IN FRONT of the Sun. Though pictures project the event in only two dimensions, a remarkable three dimensional perspective on the transit is possible by free viewing this stereo pair. The images were made 23 minutes apart and rotated so that Mercury's position shifts horizontally between the two. As a result, Mercury's orbital motion produced an exaggerated parallax simulating binocular vision. Between the two exposures, the appropriately named planet's speedy 47.4 kilometer per second orbital velocity actually carried it over 65,000 kilometers. Taken first, the left image is intended for the right...

Explanation: What's that under the surface of Mercury? The robotic MESSENGER spacecraft that had been orbiting planet Mercury for the past four years had been transmitting its data back to Earth with radio waves of very precise energy. The planet's gravity, however, slightly changed this energy when measured on Earth, which enabled the reconstruction of a gravity map of unprecedented precision. Here gravitational anomalies are shown in false-color, superposed on an image of the planet's cratered surface. Red hues indicate areas of slightly higher gravity, which in turn indicates areas that must have unusually dense matter under the surface. The...

When NASA's Mariner 10 flew by Mercury three times in the mid-1970s, it spotted what Blewett described as "certain odd, bright patches" within the impact craters. The patches showed up again during MESSENGER's flybys of the planet. It wasn't until 2011, when MESSENGER entered orbit and began to capture higher-resolution images, that the bright areas were revealed as shallow, irregularly shaped depressions on the surface. Hollows are relatively small landforms — shallow features on the surface that stretch at most 0.6 miles (1 kilometer). This small size implies a relatively young age, as cratering would have eroded them away over...

Mercury reflects very little light but its surface is low in iron, which rules out the presence of iron nanoparticles, the most likely "darkening agent". First, researchers modelled how much carbon-rich material could have been dropped on Mercury by passing comets. Then they fired projectiles at a sugar-coated basalt rock to confirm the darkening effect of carbon. Their results, published in the journal Nature Geoscience, support the idea that Mercury was "painted black" by cometary dust over billions of years. The effect of being intermittently blasted with tiny, carbon-rich "micrometeorites", the team says, is more than enough to account for...

Explanation: Inner planets Venus and Mercury can never wander far from the Sun in Earth's sky. This week you've probably seen them both gathered near the western horizon just after sunset, a close conjunction of bright celestial beacons in the fading twilight. The pair are framed in this early evening skyview captured on January 13 from the ruins of Szarvasko Castle in northwestern Hungary. Above the silhouette of the landscape's prominent volcanic hill Venus is much the brighter, separated from Mercury by little more than the width of two Full Moons. On Friday, planet Earth's early morning risers will also...

Tonight the duo will be at their closest and remain near one another for the next week or so. This is one of Mercury’s best apparitions of the year for northern hemisphere skywatchers and well worth donning your winter uniform of coat, boots, hat and thick gloves for a look. Just find a location with a decent view of the southwestern horizon and start looking about a half hour after sunset. Mercury and Venus will be about 10° or one fist held at arm’s length high above the horizon.

Missing Venus? The third brightest natural object in the heavens returns to prime time dusk skies in 2015 after being absent and lingering in the dawn for most of 2014. But there’s another reason to hunt down the Cytherean world this week, as elusive Mercury chases after it low in the dusk. If you’ve never seen Mercury for yourself, now is a great time to try, using brilliant Venus as a guide.

The most bashful of all the naked eye planets makes its best dawn appearance of 2014 this weekend for northern hemisphere observers. And not only will Mercury be worth getting up for, but you’ll also stand a chance at nabbing that most elusive of astronomical phenomena — the zodiacal light — from a good dark sky sight. DST note: This post was written whilst we we’re visiting Arizona, a land that, we’re happy to report, does not for the most part observe the archaic practice of Daylight Saving Time. Life goes on, zombies do not arise, and trains still run...

Explanation: Transits of Mercury are relatively rare. Monday's leisurely 7.5 hour long event was only the 2nd of 14 Mercury transits in the 21st century. If you're willing to travel, transits of the International Space Station can be more frequent though, and much quicker. This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station...

Explanation: On May 9, the diminutive disk of Mercury spent about seven and a half hours crossing in front of the Sun as viewed from the general vicinity of Earth. It was the second of 14 transits of the Solar System's innermost planet in the 21st century. Captured from Fulham, London, England, planet Earth the tiny silhouette shares the enormous solar disk with prominences, filaments, and active regions in this sharp image. But Mercury's round disk (left of center) appears to be the only dark spot, despite the planet-sized sunspots scattered across the Sun. Made with an H-alpha filter that...

Explanation: What's that small black dot moving across the Sun? Mercury. Possibly the clearest view of Mercury crossing in front of the Sun earlier this week was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Featured here is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Mercury' ultra-thin atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images...

Explanation: What's that dot on the Sun? If you look closely, it is almost perfectly round. The dot is the result of an unusual type of solar eclipse that occurred in 2006. Usually it is the Earth's Moon that eclipses the Sun. This time, the planet Mercury took a turn. Like the approach to New Moon before a solar eclipse, the phase of Mercury became a continually thinner crescent as the planet progressed toward an alignment with the Sun. Eventually the phase of Mercury dropped to zero and the dark spot of Mercury crossed our parent star. The situation could...

If you enjoy watching paint dry, you may enjoy the Transit of Mercury taking place right now. It is cloudy here, so we can't see it directly.

Explanation: This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006. Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun. The above time-lapse sequence, superimposed on a single frame, was taken from a balcony in Belgium shows the entire transit of 2003 May 7. The solar crossing lasted over five hours, so that the above 23 images were taken roughly 15 minutes apart. The north pole of...

Although both Mercury and Venus circle between the Earth and the sun on every orbit (with Mercury passing between the two bodies three times each Earth year), the three planets don't sit in a flat orbit compared to one another. Only when Earth and a passing planet line up is the interior world visible to skywatchers as it crosses the sun. Mercury's transits currently take place in either early May or November. It is during those months that Earth's orbital plane is intersected by Mercury's, according to NASA's Goddard Space Flight Center. However, the orientation of the two orbital planes...

Skywatchers will have many opportunities in 2016 to see just how small we are in the universe. Four days into the new year, hundreds of meteors will dance across the night skies.... Come September, an outer ring of the sun's annular eclipse will be visible across Africa. In between, there will be spectacular shooting stars, super moons, and lunar eclipses to take in. ... From about Jan. 20 to Feb. 20, all five planets that are visible to the naked eye — Mercury, Venus, Mars, Jupiter and Saturn — will occupy the morning sky. This hasn't happened since 2005, according...