Scientists have discovered the tiniest known planet, which is even smaller than Mercury, the smallest planet in our solar system. A team of scientists led by two Yale University astronomers identified the tiniest planet yet discovered. They called it YBP 676. The new planet is about the size of a dwarf planet and lies within the so-called "habitable zone" around its star, which is capable of supporting life as we know it.
YBP 676 was found using a technique called "transit photometry," which measures the drops in light from a star as an orbiting planet passes in front of it. This approach has revealed many interesting exoplanets over the years, but it can only detect large planets that pass directly across their parent stars from our perspective on Earth. Smaller worlds like YBP 676 are harder to find with this method.
However, astronomers have evidence that many small planets are actually larger than they appear from Earth due to effects such as orbital inclination or eccentricity. Using these clues, they can estimate what kind of world might be hiding behind the transiting object's radius. In this case, the researchers were able to infer that YBP 676 has a mean density between those of water and rock, making it likely that it has a relatively dense iron core surrounded by a volatile envelope of hydrogen and helium.
Mercury is the smallest planet in our solar system, while Jupiter is the biggest. They both have a metallic hue to them when seen from Earth and are covered by a thin veneer of atmosphere. However they differ in many other ways as well.
Jupiter is more than 100 times heavier than Mercury. It has a mass about 99% of Earth's mass.
Both planets orbit around the Sun in a nearly circular path, but they do so at very different distances: about 0.5 AU for Mercury, 5.2 AU for Jupiter. This difference in distance leads to differences in their orbital periods: about 58 days for Mercury, about 12 years for Jupiter.
The most obvious difference between these two planets is size. While Mercury is only 1/4th the diameter of Jupiter, it packs a much bigger punch when it comes to gravity! The gravitational force of Jupiter is about 9.8 m/s2, while that of Mercury is only 3.3 m/s2. This means that even though Jupiter is more than 100 times larger than Mercury, they experience similar forces due to their close proximity to the Sun (see table below for comparison).
Mercury is the solar system's smallest planet. (Pluto used to possess the title, but it was demoted to minor planet status.) Although its surface resembles that of our moon, the small planet has a density comparable to that of Earth. It rotates very quickly, once every 487 days.
Pluto shares some characteristics with both planets and with asteroids. It has a relatively large mass compared to other objects in the Kuiper Belt, and it has a dense core surrounded by a less-dense mantle and crust. The central part of the planet is also thought to be gaseous. However it does not appear to have any significant moons of its own.
Consequently, Pluto belongs to the class of bodies called "bodies smaller than Jupiter but larger than Mars". Although it was once considered a planet, this designation has been applied only once before, so now it is merely a label for a group of objects that show many similarities to each other but are still classified as planets by most astronomers.
In March 2006, the International Astronomical Union (IAU) voted to remove Pluto from the list of planets. Before this decision, there had been nine planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus and Neptune. Now there are eight: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn and Uranus.
Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury would be listed in order of size, from largest to smallest: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury. Since the loss of Pluto as an official planet, Mercury seems to be the smallest planet in the solar system. However, because of its small size and distance from the sun, it receives only a fraction of the radiation that we know melts ice on Earth's other planets.
However, research conducted by NASA has found evidence that suggests there might be water under the surface of Mars. If this discovery turns out to be true, then perhaps one day Mars could become a second home for humans.
As for the size of each planet, that depends on how you measure them. The best way to compare sizes between objects that are not necessarily comparable in scale is to use mass. So if we use mass instead of diameter, here's how they stack up: Jupiter - Rock & Heavy Metal, Saturn - Medium-Heavy Weight Rock, Uranus - Lightweight Rock, Neptune - Water Vapor & Ice Cubes, Earth - Medium Weight Rock.
But even using mass isn't perfect, so let's look at another comparison method: volume.
Mercury is our solar system's tiniest planet, only slightly bigger than Earth's moon. But it is also the most important planet for life as we know it: without the magnetic field it generates, humans could never survive in space.
The moon is so small relative to the rest of the planets in our solar system that it is classified as a "minor planet". It is also the smallest body known to orbit another star. By volume, the major planets are Jupiter, Saturn, Uranus, and Neptune. The minor planets include all the objects found beyond the main planets by astronomers using telescopes.
The Moon is important for several reasons. First, it provides us with the only natural source of light during the night. Without this light, living on Earth would be very difficult. The Moon also controls when rivers flow and oceans rise and fall by blocking or allowing sunlight to reach the ground. Finally, the Moon acts as a gravitational force between Earth and its orbiting objects. This effect can be seen in the Moon's influence on the tides of the oceanic plates.
These roles mean that changes to the shape of the Moon will have significant effects on Earth.