President Obama Hails NASA Pluto Flyby

President Barack Obama fired off a congratulatory tweet Tuesday (July 14) celebrating the first-ever flyby of Pluto, which NASA's New Horizons spacecraft performed earlier that day.

New Horizons zoomed within 7,800 miles (12,500 kilometers) of Pluto Tuesday morning, capturing history's first up-close looks at the far-off dwarf planet and its five known moons. Prominent scientists and supporters all over the world issued statements and speeches in celebration — including President Obama.

"Pluto just had its first visitor! Thanks ‪@NASA — it's a great day for discovery and American leadership," the president said via his official Twitter account, @POTUS.

Humanity has taken a number of big space-exploration steps since President Obama took office in January 2009 (though the missions were set in motion before his time).

For example, Obama's presidency has seen NASA launch the planet-hunting Kepler mission, which has discovered more than half of the nearly 2,000 known alien planets to date. And the first man-made orbiters of Mercury, the giant asteroid Vesta and the dwarf planet Ceres reached their destinations in the past six years.

NASA's Voyager 1 probe, which launched in 1977, became the first spacecraft to reach interstellar space in 2012. And last year, the Rosetta orbiter, built by the European Space Agency, landed a probe on the surface of a comet for the first time ever.

New Horizons' visit to Pluto marks another milestone, a visit to the last (and usually most distant) of the nine classical planets that remained unexplored — but it's also just one of many objects residing in the outer reaches of the solar system that may have stories to tell.

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+.