October 29, 2015

The Moons of Pluto

Pluto's small moons are revealed in the latest image data and analysis from New Horizons' historic encounter—these may be the best view humanity ever gets of these distant objects

By Caleb A. Scharf

Join Our Community of Science Lovers!

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

When NASA's New Horizons mission launched in January 2006 the known moons of Pluto consisted of Charon (arguably more of a binary companion than a moon), and Nix and Hydra - spanning some 42 and 55 kilometers across respectively.

Remarkably, during the spacecraft's ten year, 5 billion kilometer cruise to Pluto, astronomers were able to use the Hubble Space Telescope to spot two more natural satellites - Kerberos (announced in 2011) and Styx (announced in 2012) as tiny points of reflected light.

Hubble discovery image of the smallest moons of Pluto (Credit: NASA, ESA, L. Frattare STScI)

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

Now the data returning from the spacecraft, carefully processed and analyzed, has provided our first ever - and possibly our last ever - family portrait of all of these diminutive bodies.

A portrait of moons (Credit: NASA/JHUAPL/SwRI)

Little Kerberos turns out to be smaller than expected, and seems to consist of two 'lobes', one about 8 kilometers across, the other about 5 kilometers. Its reflectivity suggests a water ice surface. This shape also suggests that it formed by the merger of two bodies, slapping together non-destructively.

Intriguingly, a smaller Kerberos contradicts predictions from measurements of its gravitational influence on the other satellites - which indicated a more massive body. What's up with Kerberos? We don't yet know.

The best image of Kerberos we may ever get - made by combining images and software deconvolution and smoothing (Credit: NASA/JHUAPL/SwRI)

Subscribe to Support Independent Journalism

Great science journalism requires human expertise, time, effort and creativity. And it costs money. That’s why I and the journalists here at Scientific American hope you’ll join our community.

When you subscribe, you are supporting staff and freelance journalists who are passionate about telling science stories that are true, important and compelling. Our editors and reporters are often experts in their fields, which means they understand the nuances of big discoveries and can untangle the breakthroughs from the hype. With a subscription, you are also supporting rigorous fact-checking to ensure the words we publish are precise and accurate. And you’re supporting original illustrations, graphics and photos that bring you closer to an advanced laboratory, an ice sheet in Antarctica or a space mission in orbit. You’re helping us craft other types of high-quality journalism as well: Our newsletters are carefully written, edited and curated by staffers you have or will come to know and love. Our Science Quickly podcast is based on original reporting, collaboration with editors and scientists and exacting production.

Subscriptions keep this engine running so we can continue to deliver thoughtful, rigorous and independent science journalism to you. In an era of viral misinformation, this work is crucial. If you value what we do, I hope you’ll consider joining us as a subscriber

Thank you,

Jeanna Bryner, Editor in Chief, Scientific American