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Mercury is having a moment

Mercury
Color-enhanced view of Mercury. Photo: NASA/JHU-APL/Carnegie

Scientists are pushing space agencies around the world to send dedicated missions to the small, relatively unexplored planet Mercury.

Why it matters: With its odd, huge core, magnetic field and unexplained chemistry, the planet is like nowhere else in the solar system.

  • "Mercury seems to be a bit of an oddball," planetary scientist Paul Byrne told Axios.

The big picture: NASA has long-dedicated many of its limited resources to studying Mars and the Moon from close range, effectively leaving planets like Mercury, Venus, Uranus and Neptune somewhat left behind.

  • NASA's MESSENGER mission, which ended in 2015, provided a wealth of data for scientists interested in Mercury, but it also left them clamoring for answers about the small planet's chemistry and composition.

What's happening: NASA is considering establishing an assessment group that will focus on bringing scientists focused on Mercury together and will help advocate for missions.

  • "This community was focused around MESSENGER for a long time and is currently self-organizing," Shoshana Weider, support scientist in NASA's Planetary Science Division, told Axios via email. "But it is important to the community, and to NASA, that we recognize ... the efforts and interests of these scientists.”
  • The European Space Agency and Japan Aerospace Exploration Agency launched the BepiColombo mission to Mercury last year. The two spacecraft in the mission should make it into orbit around the innermost planet in 2025.

Details: MESSENGER mapped Mercury's surface and also found that about 85% of the planet’s volume is taken up by a huge metal core.

  • The ratio of potassium and thorium on Mercury also suggests that the planet may have formed elsewhere in the solar system or there could be a flaw in the models used to explain planetary formation, BepiColombo scientist Johannes Benkhoff told Axios.
  • "We thought we could predict some of what Mercury would be like, and we were wrong, so we have to go back and [re-examine] some of our basic, fundamental knowledge about the solar system," planetary geologist Brett Denevi told Axios.

What's next: Some planetary scientists hope to convince NASA to send a rover or lander to Mercury in the 2030s to study the planet from its surface to get more information about the small world than an orbiter could.

  • Scientists working with NASA will soon begin a study of what would be needed for such a mission — technically and budget-wise.

The transit of Mercury

Monday's transit of Mercury gave millions of people the chance to see the smallest major planet in our solar system in much the same way that scientists spot worlds around other stars.

The big picture: Exoplanets — planets orbiting stars other than our Sun — can be detected when a star's light dips as the planet passes across the face of its star.

Details: Mercury's transits can illuminate its exosphere — the planet's extremely thin atmosphere — for telescopes.

  • "Sodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption, we can learn about the density of gas there," NASA scientist Rosemary Killen said in a statement.
  • The Hubble Space Telescope is able to parse out some elements of exoplanetary atmospheres this way as well, by watching as the planets pass in front of their stars.
  • NASA's James Webb Space Telescope will investigate exoplanet atmospheres in even more detail after its expected launch in 2021.

ICYMI: Sorry, but transits of Mercury are relatively rare events. The next one is expected to occur in 2032.

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