Sciency Words: Lobate Scarps (Is Mercury Shrinking?)

Today’s post is part of a special series that first appeared on Planet Pailly. Every Thursday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s word is:

Lobate Scarps

Since the Solar System formed 4.5 billion years ago, Mercury has decreased in size by about 11 kilometers in radius. How do we know this? By studying wrinkly features on the planet’s surface called lobate scarps.


Mercury’s interior is cooling off, and as it cools, the planet shrinks. Unlike Earth, Mercury doesn’t have active plate tectonics, so the planet’s surface is forced to contract like a deflating balloon. Lobate scarps are long, winding ridges standing over the still deflating landscape.

Recent data from the MESSENGER space probe has allowed scientists to measure the height of these scarps. From those measurements, they’ve extrapolated the size Mercury used to be compared to the size it is now.

And it just so happens that these measurements match the theoretical predictions for how much contraction a planet like Mercury should experience due to heat loss. It’s nice when theory and observation agree. It means we’re doing something right.

Article by James Pailly.

To read all the articles in the ‘Sciency Words‘ series, visit the Planet Pailly blog.

  • Paulo R. Mendes

    This is a interesting article.

  • It might surprise you but Mercury isn’t the only shrinking “rock” out there.
    Our very own moon might be a “shrinker” too. Complete with “Lobate scraps”.
    Recently discovered cliffs in the lunar crust indicate the moon shrank globally in the geologically recent past and might still be shrinking today, according to a team analyzing new images from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft. The results provide important clues to the moon’s recent geologic and tectonic evolution. The moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the moon hot. The moon cooled off as it aged, and scientists have long thought the moon shrank over time as it cooled, especially in its early history. The new research reveals relatively recent tectonic activity connected to the long-lived cooling and associated contraction of the lunar interior.
    They estimate these cliffs, the same obate scarps as on Mercury, formed less than a billion years ago, and they could be as young as a hundred million years, Ancient in human terms, it is less than 25 percent of the moon’s current age of more than four billion years. “Based on the size of the scarps, it is estimated the distance between the moon’s center and its surface shrank by about 300 feet,

    • John Hawkins

      Well, it’s obviously the moon aliens eating the moon. Gosh, you’re so silly!

    • So if I understand you correctly; James speaking about shrinking Mercury is fine, but me saying something about the shrinking moon is silly.
      Well if that is your opinion, what else is there to say.
      Ah well I should have learned from earlier responses. No problem I will limit further responses so you do not have to be compelled to comment on my silly posts.

      • John H Reiher Jr

        The silly person is the person saying it’s silly. VR, just keep on doing what your doing!

      • I agree with John. Interesting extra info, V. It’s good to know that we can apply this term elsewhere