Mercury, named for the Roman messenger of the gods, is the smallest planet in our solar system and the closest to the sun. It's also one of our nearest neighbors — the planet can come as close as 77.3 million kilometers to Earth. In many ways, it looks like our moon with a cratered surface, rocky body and very little atmosphere. But unlike the moon, Mercury has an iron core and a dense surface. It's ironic that we know so little about this planet, though that's changing. This depiction of Mercury comes courtesy of the the MESSENGER mission and it's MASCS instrument, which studied the exosphere and the surface of Mercury for several years.

1 of 8 Transit of Mercury across the sun Photo: NASA/Bill Ingalls [CC BY-NC-ND 2.0] /Flickr Because of its close proximity to the sun, Mercury is often lost in the glare and is usually best seen from Earth only when there's a solar eclipse. From the Northern Hemisphere, you can sometimes see it at dawn or twilight. Transits of Mercury only occur a handful of times within in a century. Mercury's last transit was in 2016, and the next won't happen again until 2032. The one you see above was taken this morning, Nov. 11, 2019. The transit occurs from 7:35 a.m. to 1:04 p.m. EST — but please, don't look at the sun directly. A telescope with a solar filter is necessary to spot Mercury during a transit. (You can use solar eclipse glasses for protection, but you will need magnification.) If you don't have time to stop and see the transit live, you can watch this NASA animation to get a sense of what it's like:

2 of 8 Mercury in enhanced color Photo: NASA/JPL/Northwestern University Mariner 10 was the first spacecraft to visit Mercury in the mid-1970s. During the Mariner 10 mission, scientists saw Mercury's heavily cratered surface for the first time. Each approach Mariner 10 made to the planet only revealed the same side, so only 45 percent of the planet was mapped during that mission. Here NASA shows an improved color composite of the planet formed to highlight differences in opaque minerals (such as ilmenite), iron content, and soil maturity.

3 of 8 Mercury's craters Photo: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [public domain] /Wikimedia Commons By the time Mariner 10 had completed its mission, it had taken more than 7,000 photos of the planet. When Mariner 10 ran out of power in 1975, NASA shut it down. It's believed to be orbiting the sun.MESSENGER was next up to take a closer look. This enhanced color mosaic shows the Munch (from left), Sander and Poe craters, which lie in the northwest portion of the Caloris basin.

4 of 8 MESSENGER before flight Photo: NASA [Public domain] /Wikimedia Commons In 2004, NASA launched MESSENGER, which stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging. The purpose of MESSENGER was to pick up where Mariner 10 left off. IN 2011, MESSENGER began its orbital mission, mapping Mercury and sending back a treasure trove of images, compositional data and scientific discoveries. MESSENGER flew by Mercury three times, orbiting the planet for four years before crashing on the surface. The European Space Agency's BepiColombo mission launched in 2018, with a target date for insertion into orbit around Mercury in 2025.

5 of 8 Craters on Mercury Photo: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington MESSENGER was able to detail the planet's surface as never before. This is the Eminescu crater, illuminated by a bright halo of material around its edge. MESSENGER's goal was to answer some key questions about the planet, such as the composition of its atmosphere and conditions on its surface. Mercury is extremely dry, very hot and almost completely airless. It has no moons. The sun's rays are seven times stronger on Mercury than Earth, according to NASA, and the sun itself appears to be two and a half times as big from the surface. No evidence for life has been found there. Daytime temperatures can reach 430 degrees Celsius (800 degrees Fahrenheit) and drop to minus 180 degrees Celsius (minus 290 degrees Fahrenheit) at night. It's unlikely that life — at least as we know it — could survive on this planet.

6 of 8 Mercury's Southern Hemisphere NASA/JPL. NASA developed this composite image of Mercury's south side by using the photographs taken during the Mariner 10 mission. Just like our moon, Mercury reflects up to 6 percent of the sunlight it receives. Because it lacks a real atmosphere, Mercury is sort of like a piñata in space. Meteors don't disintegrate before connecting with the planet's surface, so impacts are powerful. But like Earth, Mercury has a mantle crust and an iron core. Mercury may have water ice at its north and south poles inside deep craters, but only in regions of permanent shadow.

7 of 8 Planetary smashup NASA/PJL/Cal-Tech. What is Mercury's fate? Experts believe that our sun will eventually expand and become a red giant in about 7.6 billion years. In doing so, the sun will absorb Mercury, Venus and probably Earth. Or perhaps the planet will be destroyed another way. Here an artist depicts a planet the size of Mercury colliding with a satellite the size of our moon. NASA has found evidence that a collision like this occurred about 100 light-years away on a planet near the HD 172555 star.