00:00You're standing next to a huge floor-to-ceiling window of the spaceship-slash-wandering city
00:06you've been calling your home for a dozen years, along with a few hundred other people.
00:11You're watching a fascinating object nearing your spaceship, wondering if it'll bring
00:15an end to this journey and your life.
00:18It looks like an asteroid, but acts like a comet, moving as if something is pushing it.
00:24Can it be the engine created by another space civilization?
00:27Are you doomed, or are you about to have contact with a different kind of intelligence?
00:32Now let's leave this post-apocalyptic fantasy and take a closer look at these space invaders
00:38called dark comets.
00:40The most intriguing question is obviously, what makes them move?
00:44Most likely, it's some gas or material escaping from the surface of these space objects.
00:49Interestingly, until recently, no one has even been sure they existed.
00:54The first dark comet was discovered just a few years ago, and since then, researchers
00:58have identified 14 of them, including 7 new ones found just recently.
01:04The story of dark comets began in 2016, when scientists noticed something strange about
01:10an asteroid called 2003RM.
01:13Its orbit wasn't quite what they expected.
01:16It had shifted slightly, and no one could explain that shift by typical asteroid behavior.
01:22And they received tiny pushes caused by sunlight hitting an asteroid unevenly.
01:26Instead, the movement suggested that 2003RM might have been releasing material, something
01:33comets often do.
01:35But there was a catch.
01:36The thing didn't look like a comet.
01:38There was no tail, no visible gas cloud.
01:41It was just a tiny dot of light, like a regular asteroid.
01:45At first, scientists thought 2003RM was just a one-off mystery.
01:50But in 2017, a telescope spotted another strange object, this one from outside our Solar System.
01:58It was Oumuamua.
01:59It too looked like an asteroid, but had a path that changed as if gas were escaping
02:05from it.
02:06The similarities between Oumuamua and 2003RM made researchers think there might be more
02:12of such odd objects out there.
02:14By 2023, seven more had been discovered in our Solar System.
02:19These discoveries were enough to give this new type of object the name of Dark Comets.
02:24Now scientists have enough data to start noticing patterns and learning more about their characteristics.
02:30And so, they have identified two main groups of Dark Comets.
02:35The first group, called Outer Dark Comets, is larger, with sizes ranging from hundreds
02:40of feet to even more.
02:42They follow long elliptical orbits, similar to traditional comets that come from regions
02:46near Jupiter.
02:48The second group, Inner Dark Comets, is smaller, usually tens of feet across.
02:53These comets move in almost circular orbits and stay closer to the Sun, near planets like
02:58Earth, Venus, and Mars.
02:59The main question these days is, where do Dark Comets come from?
03:03Can they be the remnants of larger bodies that broke apart?
03:07These space bodies could help us understand the history of the Solar System.
03:11What if they had delivered the ingredients for life to early Earth?
03:15Once we study Dark Comets better, we might figure out if they contain materials like
03:19ice or organic compounds.
03:22And indeed, some researchers are sure that Dark Comets may contain or once have contained
03:28ice and played a big role in bringing water to Earth.
03:31According to a couple of studies, some asteroids in the Asteroid Belt, a region between Mars
03:37and Jupiter filled with rocky debris, might have ice beneath their surfaces.
03:42And this ice from the Asteroid Belt could have traveled into near-Earth space.
03:46In other words, it could be a pathway for water to reach our planet.
03:51So far, no one is saying that Dark Comets definitely brought water to Earth.
03:55But they might be another mechanism for moving ice from one part of the Solar System to another.
04:02The study also hints at a connection between Dark Comets and a group known as Jupiter Family
04:08Comets.
04:09These are comets whose orbits are strongly influenced by the gravity of Jupiter, often
04:13pulling them inward toward the Sun.
04:16This connection makes it even more difficult to understand where Dark Comets come from
04:20and how they behave.
04:23Now let's take a closer look at the differences between asteroids and comets.
04:27General asteroids are rocky bodies that orbit relatively close to the Sun, typically within
04:33the ice line.
04:34This region is so close to the Sun that any ice on an asteroid's surface would turn
04:39directly from a solid into a gas, leaving behind only rock.
04:44Comets in turn are icy bodies that form farther from the Sun.
04:48When they approach the inner Solar System, their ice starts turning from a solid to a
04:52gas too, creating a visible cloud called a coma or a tail while releasing dust and gas.
04:59Dark Comets blur these definitions.
05:01They appear as rocky asteroid objects without a coma or tail, but they have behavior typical
05:07of comets, and that's small non-gravitational accelerations.
05:12These accelerations occur when ice turns into gas, giving the object a slight push.
05:17After analyzing 7 known Dark Comets, astronomers estimated that between 0.5% and 60% of all
05:25near-Earth objects might belong to this mysterious category.
05:29And since Dark Comets likely come from the asteroid belt, ice is likely to exist even
05:34in the regions of the belt previously thought to be too warm.
05:39Now near-Earth objects like Dark Comets don't stay in the same orbit forever.
05:43The near-Earth environment is unstable, and objects typically remain there for about 10
05:48million years.
05:50Since the Solar System is over 4.5 billion years old, this means that new near-Earth
05:55objects must constantly replace those that are lost.
05:59Astronomers have used computer models to simulate the movement of objects under the influence
06:04of non-gravitational accelerations.
06:07They've traced the paths of these objects over a span of 100,000 years and discovered
06:12that many ended up in the same regions where we find Dark Comets today.
06:17Do you remember that Space Rock 2003 RM, which was the first to be called a Dark Comet?
06:23It provided a particularly interesting clue.
06:26Its elliptical orbit brings it close to Earth, then out near Jupiter, before returning to
06:31Earth again.
06:33This trajectory matches what scientists would expect from a Jupiter family comet, an object
06:38that was likely knocked inward from its original orbit.
06:41Most of the other Dark Comets studied, however, seem to have come from the inner regions of
06:46the asteroid belt, closer to Mars.
06:49Dark Comets are often small and spin rapidly.
06:53Astronomers often describe them as dirty ice cubes.
06:56All because these objects are a mix of rock and ice.
06:59And when they cross the ice line, their ice begins to turn into gas.
07:03This process not only causes those small, non-gravitational accelerations, but also
07:08increases their spin rate.
07:10And the faster these objects spin, the easier they can break apart into smaller fragments.
07:15The pieces that break off also have ice.
07:18And as they spin faster and faster, they break into even smaller pieces.
07:23This process continues until you're left with very small, fast-spinning objects.
07:28This cycle of fragmentation helps explain why Dark Comets are often so tiny.
07:33But it could also mean there are more of them than we currently know about.
07:38The Dark Comet research provides new insights into the distribution of ice in the Solar
07:42System and its potential pathways into the near-Earth environment.
07:46It also raises intriguing questions.
07:49For example, how much ice remains hidden in the asteroid belt?
07:53Or could Dark Comets have played a role in delivering water or organic materials to Earth?
07:59One of the most important points is that Dark Comets may represent a significant part of
08:04near-Earth objects.
08:06If it turns out to be true, it could mean that our understanding of the population of
08:10near-Earth objects, and their potential risks for our planet, is far from complete.
08:16The processes shaping Dark Comets, from sublimation to fragmentation, could be a major factor
08:22in the evolution of icy bodies throughout the Solar System.
08:26Luckily, these days, scientists have an opportunity to combine advanced modeling with observations,
08:32which can eventually shed light on that very elusive class of objects that could have clues
08:37to the history of water and life on Earth.
08:40That's it for today!
08:42So hey, if you pacified your curiosity, then give the video a like and share it with your
08:46friends!
08:47Or if you want more, just click on these videos and stay on the Bright Side!
