NASA's Mars Reconnaissance Orbiter (MRO) continues
to probe the red planet. Utilizing its High Resolution Imaging Science
Experiment (HiRISE) equipment, the spacecraft has
focused in on dark holes on some of the martian
volcanoes.
Speculation has centered on these features being entrances
into caves. One earlier HiRISE shot stared straight down into one of these
oddities, spotting only darkness in the pit.
A subsequent flyover of that same locale imaged the
feature from a different angle – but this time the Sun was shining from the
west. What shows up this go-round is an eastern wall of the pit.
According to Mars experts, the new image confirms that
this pit is essentially a vertical shaft cut through the lava flows on the
flank of the volcano. Such pits form on similar volcanoes in Hawaii and are called "pit craters."
Back here on Earth, such pit craters don't generally
connect to long open caverns – but are the result of deep underground collapse.
From the shadow of the rim cast onto the wall of the pit, specialists calculate
that the pit is at least 255 feet (78 meters) deep. The pit is 492 x 515 feet (150
x 157 meters) across.
--Leonard David
Credit: NASA/JPL/University
of Arizona
Return each weekday for a new SPACE.com Image of the Day.
| 
