Orbit tracking reveals a 200–400 °C thermal excess beneath southern Mars
16 years of orbiter tracking point to a 200–400 °C thermal excess beneath Mars's southern highlands. Reflected-light measurements of non-transiting HD 176071 b likewise expose a water-rich structure and moving clouds. Both studies turn variations measured outside a distant world into physical models of what cannot be imaged directly, while keeping the distinction between measurement and inference clear.
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Seasonal gravity becomes an interior scan
Mars's eccentric orbit and tilted spin axis change the Sun's tidal pull through the seasons. The peer-reviewed Nature study searched for that response in 16 years of tracking data from Mars Global Surveyor, Mars Odyssey and Mars Reconnaissance Orbiter. Degree-three gravity components, expected to remain tiny in a spherically symmetric planet, departed from model values by as much as 300 per cent. After modelling the seasonal atmospheric contribution, the team explained the signal with a north–south contrast in mantle stiffness. The inferred difference in effective shear modulus exceeds 20 per cent, showing that spacecraft motion can register a broad asymmetry far beneath the surface.[1]
The temperature is inferred, not measured
Because the stiffness pattern follows the surface crustal dichotomy, the team infers a present-day 200–400 °C thermal excess in the mantle beneath the southern highlands. The range is a model-derived estimate that combines gravity data with the long-timescale behaviour of rock. The paper leaves two explanations open. Regional mantle convection could have kept warmer material beneath one hemisphere. Alternatively, the thicker southern crust may have insulated the mantle for billions of years. The gravity signal gives a strong view of the deep contrast, but it does not by itself select the historical process that produced it.[1]
Reflected light reveals a planet that never transits
HD 176071 b never passes in front of its star from Earth's viewpoint, so the usual dip-in-starlight method cannot reveal it. The study reported by Space.com instead used HARPS-N to measure how reflected light changes across the planet's 14-hour orbit. The world, about 335 light-years away, is roughly 2.5 times Earth's radius and 8.5 times its mass; that ratio points to a structure that may be about 50 per cent water. A phase shift between Kepler and TESS observations taken six years apart is interpreted as clouds forming and moving along the planet's colder edges. Its interior and atmosphere are again inferred from variation measured at a distance rather than directly imaged.[2]
