Astronomers said Wednesday that they had spotted a fifth moon orbiting Pluto, which they already knew had four. The discovery, made with the Hubble Space Telescope, gives Pluto more moons than Mercury, Venus, Earth and Mars combined. 

 

The announcement, initially conveyed on Twitter, caught the attention of some science-minded comedians on the same medium. “It’s like, since being kicked out of the planet gang, it’s decided to form a rival solar system,” said Dean Burnett, a neuroscientist and stand-up comic in Britain. “Good one Pluto, I say.” 

 

The discovery of the moon, known simply as P5 for now, by itself does not change the terms of the “Is Pluto a planet?” debate. 

 

Moons are not a prerequisite for planethood — unless one wanted to first expel Mercury and Venus, which are moonless — and many smaller bodies are also known to have moons orbiting them. 

 

But that did not stop top planetary scientists from friendly taunting on Twitter. One comment came from Michael Brown, the astronomer at the California Institute of Technology who discovered an object in the outer solar system that appeared larger than Pluto and set off the chain of events that culminated in the demotion of Pluto from planet to dwarf planet in 2006. 

The “real implication of 5+ moons for Pluto?” he wrote. “Even things which aren’t planets can be complicated and interesting. But you knew that. Right?” 

 

(Just in case you are not certain of Dr. Brown’s views, his Twitter name is “plutokiller.”) 

 

S. Alan Stern, the principal investigator of NASA’s New Horizon’s spacecraft, which is currently speeding toward a close encounter with Pluto in July 2015, wrote a tart reply: “Does CalTech cultivate old school ideas? Get used to planets unlike Earth ruling. Accept Nature. Breathe Mike. Breathe.” 

 

However, the new moon could spell trouble for Dr. Stern and New Horizons. 

 

The chances that New Horizons would crash into P5 — a tiny nugget most likely no wider than Manhattan is long — or one of the other moons are vanishingly small. But Pluto could be enshrouded by smaller debris shed by the moons. 

 

With New Horizons flying through at 30,000 miles per hour, “even small particles that weigh less than a milligram can be lethal to the spacecraft,” Dr. Stern said. 

 

The Hubble pictures of Pluto, led by Mark Showalter, an astronomer at the Seti Institute in Mountain View, Calif., were conducted to help identify safe regions for the NASA spacecraft. 

 

For now, not much is known about P5 other than that it is a speck of light, about one hundred-thousandth as bright as Pluto that orbits at a distance of 26,000 miles. 

 

The New Horizons team is coming up with a backup plan that would let it change the flyby — currently planned to pass less than 7,000 miles above the surface of Pluto — to a safer distance if it turns out that neighborhood is too cluttered. 

 

Dr. Stern said the mission would still meet all of its main objectives. “That doesn’t leave us in the poorhouse,” he said. “We don’t get some of the icing of going up close.” 

 

(Source: The New York Times)