The surface of the planet, known as HD 149026b, registered 3,700°F. Although just a bit smaller than Saturn, the planet cannot be seen separately because it is too close to the star it circles. But as it passes behind the star, the total amount of light diminishes, a clue that let the scientists deduce the planet's temperature on the side that faces the star.

The planet was discovered two years ago and is thought to be more massive than Saturn. To have such a high temperature, scientists believe the planet's atmosphere must be darker than charcoal, so it absorbs all the starlight that reaches it and reradiates that energy in the IR spectrum. "The heat would make the planet glow slightly," says Joseph Harrington, a professor at the University of Central Florida and team leader. "So it would look like an ember in space, absorbing all incoming light but glowing a dull red.

"The planet is off the temperature scale for planets, so we don't really understand what's going on," says NASA's Drake Deming, another team member. "There may be more big surprises in the future."