It’s been an exciting month for skywatchers! Last month I talked about some of the easy sights for backyard telescopes in the constellation Orion, which is looming large in our evening skies. The first couple weeks of February though, offer an even more impressive naked-eye sight in our morning sky: the possibility of glimpsing all five visible planets arranged in a straight line across much of the sky. The arrangement is best right now and will continue throughout the first week of February.

Standing outside before dawn, look to the east. Venus is bright above the eastern horizon, and if you have a clear view you may catch elusive Mercury even lower toward the Sun’s glow. Saturn is above Venus to the south, with Mars riding high in the southern sky. Jupiter is the bright object beyond Mars, toward the southwest. Altogether, the planets make a lovely arrangement that spreads across nearly the entire southern skies. The best time to look for them is just before sunrise, around 5:30 to 6:30, at which time the Sun’s glare begins to wash them out.

The mornings of this first week also bring an additional sight to the arrangement: a lovely slender crescent moon which passes by Mars on February 1^st, is near Saturn by the morning of the 3^rd, and moves down toward Venus on the 5^th. An arrangement like this, with all the planets neatly in a row along the ecliptic, is fairly rare, so make an effort to rise early and take a look at this vista of the closest worlds of our solar system.

I mentioned last month I’d spend this column talking about telescope basics, but planetary happenings are enough to push that back a bit. Besides the arrangement of visible planets, astronomers grew quite excited this week with news of new evidence that might indicate the existence of an undiscovered ninth planet in our solar system.

When you look up at the pre-dawn sky this week, you can see all the visible planets in our solar system, which are all the planets that were known throughout most of history. It was only in the late 1700s that we began to realize there were other planets in our own backyard, and this most recent announcement may herald that our family of planets is about to expand again, for the first time in over a century.

All of this obviously makes astronomers pretty excited but also cautious, as there have been lots of false claims for Planet X in the past.

Until William Herschel stumbled upon Uranus in his telescope sights in 1781 and subsequent calculations showed that it wasn’t something like a comet, Saturn was considered the outer boundary of our planetary system. As astronomers observed the new planet though, they eventually realized that something was causing it to speed up and slow down in its orbit. The French astronomer Le Verrier correctly deduced that this was caused by an additional planet in our solar system and predicted its location, and Neptune was thus discovered in 1846.

Since then, astronomers on and off have believed they’ve seen evidence in the motions of the outer planets to hint at other planets lurking out there in the darkness. It was while searching for such a world that Illinois native Clyde Tombaugh found Pluto in 1930. However, it was later realized that Pluto was far too small to be causing any gravitational perturbations and in fact the perturbations themselves didn’t actually exist.

But this is where things get interesting, because it turned out that Pluto was actually simply the first in an entire class of tiny, distant solar system bodies called Kuiper Belt objects. Indeed, it was the discovery of more and more of these objects—some farther away and more distant than Pluto—that eventually caused Pluto to be reclassified as a dwarf planet.

Now, two astronomers from Caltech have published a paper arguing that the orbits of a handful of Kuiper Belt objects show evidence for an even larger body, about the size of Neptune, in the far reaches of the solar system. The reasoning is similar to that which led to the discovery of Neptune: it appears as though a large, massive object is affecting the orbits of these objects. Mathematical modeling indicates these observations could be explained by a ninth planet.

Of course this doesn’t mean that it’s there for sure. That’s how science works: observations provide evidence, and scientists offer a theory or hypothesis to explain it. A good hypothesis is one that can be tested. And that’s exactly what’s happening now: telescopes are being trained toward the outer reaches of the solar system to see if this posited body does indeed exist. If it does, it should be large enough to spot in very large telescopes, despite its enormous distance.

And if it is spotted, the total number of planets in the solar system will go back up to the number we learned in grade school.

This column originally appeared in the Kankakee Daily Journal.