The contraction of Mercury occurs on tremendous timescales, so it's unlikely that much would change in a matter of years. Still, some questions remain about the incredible shrinking planet.
Large fault scarps on Mercury were first discovered in the flybys of Mariner 10 in the mid-1970s and confirmed by MESSENGER, which found the planet closest to the sun was shrinking.
Over the billions of years since its formation at the birth of the solar system, the planet has slowly cooled, a process all planets suffer if they lack an internal source of heat renewal. As the liquid iron core solidifies, it cools, and the overall volume of Mercury shrinks.
The most widely accepted model of the origin of Mercury's large fault scarps is that they are essentially wrinkles that formed as the planet's interior cooled over time. The cooling caused Mercury to shrink, in turn shriveling its crust like the skin of a raisin.
Like a raisin spinning around the sun, Mercury is shrinking and wrinkling. The planet is now up to 8.6 miles (14 kilometers) smaller in diameter than it was nearly four billion years ago, according to a report released on Sunday. The planet is downsizing because it is cooling.
Saturn's rings are disappearing, and we don't know how much longer they will be around. Astronomers have known since the 1980s that Saturn's icy innermost rings are steadily eroding onto its upper atmosphere.
Now, the good news: there's only about a 1% chance that Mercury will go crazy before the Sun bloats into a red giant billions of years from now. "If you're an optimist," says Laughlin, "then you say the glass is 99 percent full."
Pluto has been shrinking at an alarming rate for some time now. Well, not actually shrinking—rather, our awareness of how small Pluto is has been growing. Upon its discovery, in 1930, scientists trumpeted that Pluto was about as large as Earth.
Thanks to our leaky atmosphere, Earth loses several hundred tons of mass to space every day, significantly more than what we're gaining from dust. So, overall, Earth is getting smaller.
This slow but constant loss of mass from Jupiter's atmosphere is actually greater than the gain in mass from collisions so, overall, Jupiter is shrinking not growing in mass.
Because of Earth's gaseous gifts to space, our planet — or, to be specific, the atmosphere — is shrinking, according to Guillaume Gronoff, a senior research scientist who studies atmospheric escape at NASA's Langley Research Center in Virginia. However, we're not shrinking by much, he said.
But Mercury doesn't have much of a molten core. It's so small that its inner core has completely cooled off by now and is now rock solid. It still maintains a little bit of a liquid outer, core, however, but it's not exactly big.
Long, steep cliffs formed when Mercury's core cooled, shrinking the planet by ~20 km. Mercury is now geologically dead.
The spin of Earth's inner core may have slowed, with the heart of the planet now rotating at a slightly more sluggish clip than the layers above, new research finds. The slowdown could change how rapidly the entire planet spins, as well as influence how the core evolves with time.
Essentially, Pluto had residual heat from when it was closer to the sun. However, the inertia starting to wear off and, as Pluto gets colder, more and more of its atmosphere will freeze back onto its surface and "disappear."
Right now, the reason Earth is stable against gravitational collapse is because the forces between the atoms that make it up — specifically, between the electrons in neighboring atoms — is large enough to resist the cumulative force of gravity provided by the entire mass of the Earth.
Overall, the Earth isn't even spiraling in toward the Sun; it's spiraling outward, away from it. So are all the planets of the Solar System. With every year that goes by, we find ourselves just slightly — 1.5 centimeters, or 0.00000000001% the Earth-Sun distance — farther away from the Sun than the year before.
However, our planet also loses weight. Hydrogen gas that escapes into the Earth's gravity is so light that gravity cannot retain it in the atmosphere. About 90,000 tonnes of hydrogen escapes the Earth annually. The resulting 50,000 tonne loss is fairly insignificant, given the total mass of the planet.
Over millions of years, Earth's rotation has been slowing down due to friction effects associated with the tides driven by the Moon. That process adds about about 2.3 milliseconds to the length of each day every century.
The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.”
"If Pluto disappeared, it certainly wouldn't have an effect on Earth," says Sarah Hörst, a planetary scientist at Johns Hopkins University. Gravity depends on mass, and the force it exerts decreases over distance. Pluto is too tiny, and too far, to affect Earth.
Human travel to Pluto is out of the question, at least in the near future. It would take too long and be too hard to pack things like food for so many years. We need to be able to travel faster so the trip won't take so long.
Mercury will be swallowed by the Sun during its first red giant phase. Venus may survive the first phase, but will be consumed during the second giant phase. In all but the direst scenarios, Mars will survive the Sun's final stages of evolution.
Theia is a hypothesized ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, with some of the resulting ejected debris gathering to form the Moon.