One shocking fact about each and every planet in the Solar System

Do you truly know our Solar System?

The hematite spheres (or ‘Martian blueberries’) as imaged by the Mars Exploration Rover. These are almost certainly evidence of past liquid water on Mars, and possibly of past life. NASA scientists must be certain that this site – and this planet – are not contaminated by the very act of our observing. As of yet, there is no surefire evidence for either past or present Martian life.

Each world holds secrets that typically go unrecognized.

The northern polar aurorae seen on Jupiter, as imaged here with Hubble’s NICMOS camera, represents a cyclotron-driven maser: the first such one detected from a planetary body within our own Solar System.

Can you identify all 10?

The surfaces of six different worlds in our Solar System, from an asteroid to the Moon to Venus, Mars, Titan, and Earth, showcase a wide diversity of properties and histories. While only Earth is known to contain liquid water rainfall and large cumulations of liquid water on its surface, other worlds have other forms of precipitation and surface liquids, both at present and also in the distant past. Perhaps, long ago, Earth was joined by other worlds or even other planets, such as Mars and Venus, in possessing liquid water and perhaps life on its planetary surface.

1.) I’m the hottest planet.

The WISPR data from the Parker Solar Probe, in monochrome, clearly matches the surface features seen by the infrared orbiter Magellan, shown in assigned color. Long wavelength light, such as infrared light, can peer through the clouds of Venus, all the way down to the surface. It’s only because the clouds themselves radiate in the infrared that phosphine can act as an absorber along the line-of-sight.

The atmospheric greenhouse effect on Venus yields consistently higher temperatures than Mercury.

The Soviet Union’s series of Venera landers are the only spacecraft to ever land and transmit data from the surface of Venus. The longest-lived of all the landers exceeded the two-hour mark before the instruments overheated and contact was lost. To date, no spacecraft has survived for longer on the Venusian surface, where temperatures reach 900 degrees Fahrenheit (482 °C).

2.) I’m the most metallic planet.

When it comes to the large, non-gaseous worlds of the Solar System, Mercury has by far the largest metallic core relative to its size. However, it’s Earth that’s the densest of all these worlds, with no other major body comparing in density, owing to the added factor of gravitational compression. Unlike Venus, Earth, and Mars, Mercury has no separate crustal layer to speak of.

An early vapor state ensured Mercury is ~75% metal, by mass.

The above image shows an orthographic projection of planet Mercury in this global mosaic centered at 0°N, 0°E. The rayed crater Debussy can be seen toward the bottom of the globe and the peak-ring basin Rachmaninoff can be seen toward the eastern edge. Mercury is the Solar System’s innermost and smallest planet, and was mapped in detail by NASA’s MESSENGER mission.

3.) I’m originally the 8th planet.

The dwarf planet Ceres, shown here, is the largest world in the asteroid belt and the only one known, for certain, to be in hydrostatic equilibrium. Discovered in 1801 by Giuseppe Piazzi, it was originally classified as a planet: the Solar System’s 8th.

Ceres, discovered in 1801, is the asteroid belt’s lone dwarf planet.

The four largest asteroids, all shown here, have been imaged with NASA’s Dawn mission and the ESO’s SPHERE instrument. Ceres, the largest asteroid, is the smallest known body in hydrostatic equilibrium. Vesta and Pallas are not, but Hygeia’s status is indeterminate; it may yet be.

4.) My planetary system contains the most water.

By size, it’s clear that the gas giant worlds vastly outstrip any of the terrestrial planets, and this is true for mass as well. Although Saturn is nearly the same physical size as Jupiter, it contains just 21% of the planetary mass in the Solar System, compared to Jupiter’s whopping 71%.

That’s Jupiter, whose moons Ganymede, Callisto, and Europa individually possess more water than Earth.

Although Earth contains the most liquid water on its surface of any of the 8 planets, the most water in any form is found on Jupiter’s moon Ganymede. Next in order is Saturn’s Titan, Jupiter’s Callisto, and Jupiter’s Europa. Planet Earth has only the 5th most water, placing it ahead of Pluto, Dione, Triton, and Enceladus, which land in 6th through 9th place in the Solar System, respectively. Other, more poorly explored Kuiper belt objects, such as Eris, may yet deserve a place on this list.

5.) I’m the most massive object originating from the Kuiper belt.

Triton’s south polar terrain, as photographed by the Voyager 2 spacecraft and mapped to a spheroid of the appropriate shape and size. About 50 dark plumes mark what are thought to be cryovolcanoes, with those trails being caused by the phenomenon colloquially called ‘black smokers.’ Triton is a captured Kuiper belt object, having most certainly cleared out almost all of Neptune’s original moons.

Neptune’s captured moon, Triton, surpasses Pluto and Eris in both mass and size.

Although Earth and Venus are the two largest rocky objects in the Solar System, Mars, Mercury, as well as over 100 of the largest moons, asteroids, and Kuiper belt objects have all achieved hydrostatic equilibrium. Ganymede and Titan are larger than Mercury, but Callisto, at 99% of Mercury’s size, has just one-third of Mercury’s mass. All told, all known objects with radii greater than 800 km are in hydrostatic equilibrium, but below that threshold, it isn’t a certainty any longer.

6.) I’m the lowest density planet.

When we classify the known exoplanets by both mass and radius together, the data indicates that there are only three classes of planets: terrestrial/rocky, with a volatile gas envelope but no self-compression, and with a volatile envelope and also with self-compression. Anything above that becomes first a brown dwarf and then a star. Planetary size peaks at a mass between that of Saturn and Jupiter, although there are a few “puffy” super-Jupiters, with a likely unusually light composition.

At 0.687 g/cm³, Saturn is the only planet less dense than water.

Saturn, as photographed here by Cassini during the 2008 equinox, isn’t quite round (as it’s more of an oblate spheroid), but is in hydrostatic equilibrium. With its low density and rapid rotation, Saturn is the most flattened planet in the Solar System, with an equatorial diameter that’s more than 10% larger than its polar diameter. Its colors and “bands” are largely due to different atmospheric layers appearing dominant in visible light at different latitudes.

7.) I possess the strongest winds.

These images of Neptune, from October 7, 2017 with the Hubble Space Telescope, shows the presence of clouds, bands, and varying colors and temperatures across Neptune’s upper atmosphere. The rapid changes reveal Neptune’s wind speeds: the fastest in the Solar System.

With speeds over 1,100 mph (492 m/s), Neptune’s winds are unsurpassed.

Neptune, the 8th and outermost planet in our Solar System, as imaged by Voyager 2 during its 1989 flyby of the planet. Neptune is about four times the diameter of Earth, but a much deeper blue in color than our planet. The high-altitude clouds travel at remarkable speeds: up to 1900 km/hr, while the blue color comes from copious amounts of methane gas: reflective in visible light, but an outstanding absorber in infrared light.

8.) My fragments contaminate Earth.

This scanning electron microscope image of a fragment of the Allen Hills 84001 meteorite contains inclusions that resemble simple life found on Earth. Although this sample is thoroughly inconclusive, bombardment of Earth by extraterrestrial objects is a certainty. If they contain dormant or fossilized life, we could discover it via this method.

It’s Mars; 3% of all terrestrial meteorites originate there.

Winds at speeds up to 100 km/hr travel across the Martian surface. The craters in this image, caused by impacts in Mars’ past, all show different degrees of erosion. Some still have defined outer rims and clear features within them, while others are much smoother and featureless, evidence of old age and erosion. On Earth, a small but significant percentage of our meteorites originate from Mars; it is unknown what fraction of Martian impacts originate from Earth-based rocks, and whether life stowed-away on any of them.

9.) I change the most from solstice to equinox.

Infrared images of Uranus (1.6 and 2.2 microns) obtained on Aug. 6, 2014, with adaptive optics on the 10-meter Keck telescope. The white spot is an extremely large storm that was brighter than any feature ever recorded on the planet in the 2.2-micron band. The cloud rotating into view at the lower-right limb grew into a storm that was so large, it was visible even to amateur astronomers at visible wavelengths. These features were not present in 1986, when Voyager 2 flew by Uranus.

It’s Uranus, whose 97° axial tilt causes planet-wide changes every 21 years.

Although this is a modern, infrared view of our Solar System’s 7th planet, it was only discovered in 1781 through the serendipitous observations of William Herschel. We can see bands, clouds, aurorae, storms, and more when Uranus is near equinox, but it appears largely featureless when viewed near solstice.

10.) I’m the final planet to form.

A synestia doesn’t just consist of this puffy ring/torus of debris around a joint planetary core, but also rises to high temperatures in excess of 1000 K, causing it to emit substantial amounts of its own infrared radiation, with peaks in different parts of the infrared spectrum dependent on the exact temperature and temperature profile of the system in question. The heat from the early Earth, which may have been just 24,000 km away from the Moon initially, would have played a role in heating the Earth-facing side of the Moon.

It’s us! An impact 50 million years after the other planets formed created today’s Earth-Moon system.

Japan’s Kaguya probe went to and orbited the Moon, which enabled magnificent views of the Earth seen over the lunar surface. Here, the Moon is photographed along its day/night boundary, the terminator, while Earth appears in a half-full phase. From the near side of the Moon, the Earth is always visible; both are the result of the aftermath of an early, giant impact between a Mars-sized protoplanet and a proto-Earth.

Mostly Mute Monday tells an astronomical story in images, visual, and no more than 200 words. Talk less; smile more.