![]() Agol said the answer might be a combination of the two scenarios - less iron overall and some oxidized iron. The surface of Mars gets its red tint from iron oxide, but like its three terrestrial siblings, it has a core composed of non-oxidized iron.īy contrast, if the lower density of the TRAPPIST-1 planets were caused entirely by oxidized iron, then the planets would have to be rusty throughout and could not have iron cores. The additional oxygen would decrease the planets’ densities. For example, one way to explain the lower density is that the TRAPPIST-1 planets have a similar composition to Earth, but with a significantly lower percentage of iron - about 21% compared to Earth’s 32%, according to the study.Īlternatively, the iron in the TRAPPIST-1 planets might be combined with high levels of oxygen, forming iron oxide, or rust. The difference in density between the TRAPPIST-1 planets and Earth, Venus and Mars, may seem small - that 8% - but it is significant on a planetary scale. By subtracting the effect of gravity, scientists can calculate what’s known as a planet’s uncompressed density and potentially learn more about a planet’s composition. Even the four terrestrial worlds show some variety in their densities, which are determined by both a planet’s composition and compression due to the gravity of the planet itself. The gas-dominated giants – Jupiter, Saturn, Uranus, and Neptune – are larger but much less dense than the four terrestrial worlds because they’re composed mostly of lighter elements like hydrogen and helium. In contrast to the Trappist-1 system, the densities of the eight planets in our own solar system vary widely. Together, width and weight reveal each object’s density, and from there it is possible to infer that the baseball is made of something lighter (string and leather) and the paperweight is made of something heavier (usually glass or metal).” As described in a release: “Consider that a paperweight might be about the same size as a baseball yet is usually much heavier. The more precisely scientists know a planet’s density, the more limits they can place on its composition. The new paper offers the most precise density measurements yet for any group of exoplanets. Previous calculations determined that the planets are roughly the size and mass of Earth and thus must also be rocky, or terrestrial – as opposed to gas-dominated, like Jupiter and Saturn. Repeated observations of the starlight dips combined with measurements of the timing of the planets’ orbits enabled astronomers to estimate the planets’ masses and diameters, which were in turn used to calculate their densities. Agol and UW co-authors Zachary Langford and Victoria Meadows, a professor of astronomy, analyzed data and performed computer simulations that constrained the orbits of the TRAPPIST-1 planets and calculated their densities.Īll seven TRAPPIST-1 planets, which are so close to their star that all seven would fit within the orbit of Mercury, were found via the transit method: Scientists can’t see the planets directly (they’re too small and faint relative to the star), so they look for dips in the star’s brightness created when the planets cross in front of it. The team - which includes scientists based in the United States, Switzerland, France, the United Kingdom and Morocco - used observations of the starlight dips and precise measurements of the timing of the planets’ orbits to make their detailed measurements of each planet’s mass and diameter, and from there to determine its density. “TRAPPIST-1 has a different ‘recipe’ for forming terrestrial planets, and a more uniform recipe as well,” he told me. What Agol considers the team’s most robust conclusions: The Trappist-1 planets have a “common make-up” just as the rocky planets in our solar system do, but are nonetheless in some significant ways different from our rocky planets. “This is the information we needed to make hypotheses about their composition and understand how these planets differ from the rocky planets in our solar system,” said lead author Eric Agol of the University of Washington. It may not seem like a lot, but to astrophysicists it is. This provides a goldmine of information for scientists.Įqually exciting, while the seven Trappist-1 planets have similar densities, they are 8% less dense than they would be if they had the same chemical composition as our planet. While the planets are somewhat different sizes, they appear to be all almost the exact same density. The Trappist-1 planets have been a major focus of study since its first planets were discovered in 2016, and now a new and rather surprising finding about the density of the planets has been accepted for publication in the Planetary Science Journal.
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