Data from New Horizons does not match what is seen from Earth

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The uncertainty of science: Planetary geologists are presently baffled by a conflict in the atmospheric data between New Horizons and data gathered from Earth.

On 29 June, a few weeks before the fly-by, Young organized astronomers across New Zealand and Australia to watch Pluto as it passed in front of a distant star. Tracking how the star’s light faded during the passage provided information on how much gas is in Pluto’s atmosphere. Using the same method, planetary scientists have seen the atmosphere grow denser since 1988 — and analysis of the 29 June observations shows that the trend remains intact. Young calculates that the current atmospheric pressure at Pluto’s surface is 22 microbars (0.022 pascals), or 22-millionths the pressure at sea level on Earth.

But on 14 July, New Horizons measured Pluto’s surface pressure as much lower than that ­— just 5 microbars. “How we link the two, we’re still working on,” says Cathy Olkin, a deputy project scientist for New Horizons at SwRI.

The difference could simply be that Pluto’s atmosphere is not smooth, that some regions are dense while others are thin, and New Horizons happened to look at a thin place. The Earth observations don’t have the resolution to separate the two.

There are other proposals to explain the problem. Regardless, the answer is likely hidden in the data from New Horizons that has still not been downloaded back to Earth. In a few months, all might very well become clear.

Or not, as is the natural state of science.

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