Many of the solar systems' planets and larger moons started out volcanic. A few, most obviously Earth and Io, still are. However, lunar volcanism appears to have died out more than a billion years ago, while on Mars the most recent signs appear to be a few million years old. The legacy is visible in the enormous Martian volcanic mountains and the Moon's “seas” of basalt, but nothing of the sort has been seen on either object today.
Volcanism is the result of a molten core. With no new heat source, cores would naturally cool within a few hundred million years at most, leaving the entire solar system geologically dead. In the case of Io, and moons like Enceladus, which have geysers, the heat is supplied through tidal flexing.
On Earth the remaining heat is primarily the result of the radioactive decay of elements such as uranium and thorium within the core. However, the smaller a celestial body is, the more quickly heat will escape, eventually reaching a point at which declining radioactivity is not enough to keep the core molten.
Venus is much closer to the mass of Earth than to Mars, so it is expected to still be active. The heat blanket from astonishing surface temperatures won't do any harm, either. Nevertheless, spotting evidence through the thick Venusian clouds has been a challenge.
Last year, the European Space Agency's Venus Express orbiter saw evidence of temperatures of 800°C (1500°F) near Maat Mons, which, even by Venutian standards, is hard to explain except as evidence of geological activity. Maat Mons is the largest volcanic mountain on Venus, but whether it has erupted recently is still unknown. The observations weren't considered definitive given the difficult conditions under which they were made.
Now, more powerful evidence has been found a few thousand kilometers to the north. Professor James Head, of Brown University, reports multiple examples of temperature spikes of several hundred degrees lasting just a few days, as with lava flows on Earth.
"We were able to show strong evidence that Venus is volcanically, and thus internally, active today," said Head in a statement. The hot areas range from 1 square kilometer to more than 200 times larger, and lie with in the huge rift zone known as Ganiki Chasma.
“We knew that Ganiki Chasma was the result of volcanism that had occurred fairly recently in geological terms, but we didn't know if it formed yesterday or was a billion years old,” said Head.
Head considers the hotspots particularly convincing because they occur at locations already identified as being particularly young deposits of lava. “This discovery fits nicely with the emerging picture of very recent activity in Venus’ geologic history,” said Head. Other evidence for current volcanism comes in the form of brief sulfur dioxide spikes in the Venusian atmosphere, but this may be the most powerful yet.