The National Aeronautics and Space Administration's (NASA) Curiosity rover takes a brief moment's respite from its assigned duty of exploring the Martian environment to look up at the sky, only to capture images of Mercury transiting in front of the sun.
The Jet Propulsion Laboratory (JPL) of the California Institute of Technology, which developed the six-legged rover and manages the mission for NASA's Mars Science Laboratory, showed images taken by the telephoto camera of Curiosity's Mast Camera of Mercury as a darkened spot moving in front of a much larger sun. The photos also showed two sun spots approximately the size of Earth moving much more slowly in conjunction with the rotation of the sun.
"This is a nod to the relevance of planetary transits to the history of astronomy on Earth," says Mark Lemmon of Texas A&M University, College Station, a member of the Mastcan science team. "Observations of Venus transits were used to measure the size of the solar system, and Mercury transits were used to measure the size of the sun."
The images show that Mercury takes up only about one-sixth of an entire pixel, which is why it does not take a distinct shape or form on screen. However, scientists at JPL have confirmed that the fuzzy object crossing in front of the sun is indeed the tiny planet based on calculations of Mercury's orbital path.
Curiosity recorded the planetary transit on June 3 from its station in Gale Crater on Mars. This is the first observation of a planet transiting in front of the sun made from another planet other than Earth, and the first record of Mercury in transit as seen from the red planet. In 2012, observers on Earth saw Venus in transit for the last time this century, but we can still wait for May 9. 2016 to see Mercury cross in front of the sun.
Mercury and Venus, not to mention Earth, in transit are visible far more often on Mars. The next visible transit of Mercury will occur in April 2015, while Venus will be seen from Mars crossing in front of the sun in August 2030. The Earth will go in transit in November 2084 and we'll see what images Curiosity's successors, or perhaps the Martian colonies, will take of the Earth's transit till then.
Aside from planetary transits, Curiosity has captured a number of phenomenal sightings from its vantage point on Gale Crater, including pictures of the Martian moon Phobos transiting in front of the sun, a video of Phobos and the other moon Deimos eclipsing each other, and a stunning picture of a bright star called Earth and its moon.