A European-Japanese spacecraft has beamed back some of the best close-up photos yet of Mercury's north pole as part of only the second human survey of our solar system's innermost planet.

And as MESSENGER also taught us, Mercury is shrinking. Gas giants Jupiter Neptune New Horizons Outer planets Spaceflight Voyager 2 Get the best tech, science, and culture news in your inbox daily.

The relative size of the inner planets of our solar system: Mercury, Venus, Earth and Mars. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert!