Sky & Telescope - July 2022 - 4

SPECTRUM by Peter Tyson
Joining an Elite Club
IMAGINE DISCOVERING a new planet. I'm not talking an extrasolar
planet - we've identified thousands of those in recent years - but a
new planet in our own solar system.
The last time that occurred is coming up on a century ago, when
Clyde Tombaugh collared Pluto. Of course, Pluto lost its planet
status in 2006, so officially the last time someone sighted a new planet was in
1846, when the French astronomer Urbain Le Verrier mathematically predicted
the location of Neptune and, soon after, his German counterpart Johann Galle
became the first person to knowingly lay eyes on it.
Before that came British astronomer William Herschel's discovery of Uranus
in 1781. Thus, just two planets have turned up in our star's domain in the last
quarter millennium. All the other planets beyond our own - Mercury, Venus,
Mars, Jupiter, and Saturn - have been known since antiquity.
Astronomers have roped in dozens of moons and minor planets over the centuries.
Galileo kicked things off with his discovery of the four Galilean moons
of Jupiter in 1610. Then followed Titan (Huygens, 1655), four more Saturnian
moons (Cassini, 1670s and '80s), and two each for Uranus and Saturn (Herschel,
1780s). Since 1800, myriad other small worlds
beholden to the Sun have come to our attention,
including some you might never have heard of, such as
the dwarf planets Orcus, Quaoar, and Gonggong.
But no new major planets. Isn't it high time to find
the next one in our far-flung system, if such exists?
That's a big if, as Christopher Crockett spells out in
pArtist's impression
of Planet X, with Sun in
distance
his article about the feverish search for the so-called
Planet X (page 14). Some of today's leading discoverers
of minor planets in the outer solar system contend
that an undiscovered world perhaps two to four times Earth's diameter might be
lurking there. It's based on the way something seems to be corralling a bunch of
those minor planets in a certain way. As Crockett explains, other, equally qualified
researchers doubt such a planet exists.
If it does, imagine the impact its confirmation would have: All those illustrations
depicting the eight official planets would need revising again - except this
time, the ninth planet would lie roughly 10 times farther out than Pluto. Planetary
scientists would suddenly have another quarry to study. The IAU would
have to decide on a name, which would quickly become a household one.
The hunt is on, and it's a nail-biter. If a new world does turn up, would it
change how we view our place in the cosmos? It's been so
long since another of its ilk was found, who can say?
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4
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Sky & Telescope - July 2022

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