Kepler-1547 b: A Year Shorter Than a Single Earth Day
Somewhere, a full year passes before a single day and night on Earth has run its course. That somewhere is Kepler-1547 b, a small terrestrial planet that NASA’s Kepler space telescope caught crossing its star’s face, announced in 2016.
The measuring stick: an orbit under 17 hours
One full lap of Kepler-1547 b around its star takes 16 hours and 38 minutes, 0.693 Earth days, measured directly from how regularly the transit repeats. Earth needs 24 hours just to turn once on its axis, day and night together, and this planet’s entire year fits inside that single spin with time to spare. The reason is proximity: Kepler-1547 b orbits about 1.53 million miles (2.47 million km) from its star, a distance of 0.0165 astronomical units, one astronomical unit being the roughly 93-million-mile (149.6-million-kilometer) stretch from Earth to the Sun. That puts Kepler-1547 b about 60 times closer to its star than Earth is to the Sun.
How we know
No telescope has ever photographed Kepler-1547 b. What Kepler caught was a star dimming by a sliver, over and over, every 16 hours and 38 minutes, as the planet’s disk crossed the star and blocked a fraction of its light, logged as part of Kepler’s May 10, 2016, data release. From the depth and timing of that dimming, astronomers worked out a radius of about 0.90 Earth radii, roughly 3,563 miles (5,734 km) against Earth’s own 3,959 miles (6,371 km), though the uncertainty is wide enough to put the real value anywhere from 0.78 to 1.18 Earth radii. NASA’s catalog also lists a mass of 0.666 Earth masses. For a planet known only through its shadow, a figure like that is typically modeled from the star’s own measured properties rather than weighed directly through a radial-velocity wobble, the public catalog entries don’t say which method was used here. The host star itself is cataloged as F-type, with 1.18 times the Sun’s radius, 1.12 times its mass, and a surface temperature of 6,078 kelvin.
The number that doesn’t check out
A figure of 3,186 kelvin circulates for this planet’s equilibrium temperature, the modeled heat a bare surface would settle at from starlight alone, assuming some fraction of that light bounces straight back into space (its albedo) and no atmosphere traps the rest. It’s a dramatic number, the kind that gets repeated, and it would make Kepler-1547 b’s surface genuinely extreme. But a check of three independent sources, NASA’s own exoplanet catalog page, the Open Exoplanet Catalogue, and a separate, independently maintained exoplanet archive, found the equilibrium temperature field blank for Kepler-1547 b in all three. No safe comparison can be built on a number nobody has actually published. Until that figure turns up in the NASA Exoplanet Archive’s composite parameters table with a calculation behind it, the honest answer is that nobody has published a confirmed surface temperature for this planet, not 3,186 kelvin, not anything else. What’s confirmed instead is the geometry that would drive any such heat: a world roughly Earth’s size, parked 60 times closer to its star than Earth sits from the Sun.
What’s still open
Some of the basics disagree across catalogs too. NASA’s own page lists the orbit as a perfect circle, zero eccentricity, while an independent mirror of the same measurements leaves that field blank. The system’s distance isn’t settled either: one catalog puts the host star at 688 parsecs, about 2,244 light-years, give or take 20, while another puts it closer, at 665 parsecs, roughly 2,168 light-years using the standard conversion of one parsec to 3.26 light-years. A light-year measures distance, 5.88 trillion miles (9.46 trillion km), never time, but the two catalogs still disagree by about 76 light-years’ worth of it. What’s solid is the orbit’s speed: a planet close enough and fast enough that its year fits inside one Earth day. What’s open is everything that depends on just how hot that closeness actually makes the surface, and until someone publishes that number with its method attached, it’s a question worth holding onto rather than answering with a figure that isn’t really there.