>>NARRATOR: It turns out that Ceres, the first and largest
asteroid discovered in the main asteroid belt, surprisingly has
been geologically active within the past billion years.
[music]
NASA’s Dawn spacecraft arrived at dwarf
planet Ceres in March, 2015. >>OTTAVIANO: We were expecting
an inert rocky body. >>LUCY: We expected Ceres to be a
cold rock. >>NARRATOR: One intriguing feature Dawn
discovered on the surface of Ceres is an enormous, lone
mountain the team named Ahuna Mons. >>OTTAVIANO: We have
been looking in detail about the shape of the mountain.
>>LUCY: It was very tall and had steep slopes. And that reminded us of
certain places in the solar system, including Earth and
Mars, that had domes that were formed by volcanic activity.
>>OTTAVIANO: And we have found that Ahuna Mons’ shape is very
similar to that of a volcanic dome. >>NARRATOR: Along with the
shape of the dome, the facts are that there is no evidence of
another formation mechanism such as an impact crater, and the
surface features on the summit and sides of the mountain look
incredibly similar to known volcanic domes. This all
provides substantial evidence that Ahuna Mons is in fact of
volcanic origin. Volcanoes on earth are fueled by magma
composed of molten rock. But Ceres is far too cold to melt
silicate rock in its interior. >>LUCY: We then concluded that
the magma had to be composed of mostly very salty water, and when
exposed to the surface, they would freeze and form this
steep-sided dome. >>NARRATOR: A volcano made of water or other
ices instead of rock is called a cryovolcano. Scientists have
detected evidence of cryovolcanic activity before -
plumes from Saturn’s moon Enceladus and Neptune’s moon
Triton and volcanic-looking mountain ranges on Saturn’s moon
Titan. The salty muddy mountain Ahuna Mons is yet
another new form of cryovolcanic activity discovered.
>>LUCY: There’s no other place in the solar system that has a
structure like Ahuna Mons, and it has to be formed by
cryovolcanic activity. >>NARRATOR: Moons around gas
giants can heat up from the frictions of interactingtheir
orbits, but the isolated dwarf planet Ceres is so small and
cold that we wouldn’t have thought it could have liquid
water in its recent past. Evidence suggests, however,
that Ahuna Mons is a relatively young feature.
>>OTTAVIANO: First of all, the surface is very bright, and as surfaces get
darker with time, it’s brightness tells us it’s a young
feature. And second, we see very crisp morphologies, very sharp
features, and this also tells us it’s young, as the features get
muted and smooth with time. And third, we have been looking at
crater density and we see very low density of craters. And this
tells us that Ahuna Mons was formed within the last billion
years of Ceres’ history. Ahuna Mons is evidence that Ceres was
active in the recent past and might still be active today.
>>LUCY: That tells us that there has to be something beneath the
surface of Ceres near Ahuna Mons that heated the material to the
melting point and made it push through the cracks on the
surface. >>NARRATOR: The source of this heat is still an
intriguing mystery that planetary scientists are anxious to solve.
[beep beep, beep beep...] [music fades out]