You could say that the study of extrasolar planets is in a phase of transition of late. To date, 4,525 exoplanets have been confirmed in 3,357 systems, with another 7,761 candidates awaiting confirmation. As a result, exoplanet studies have been moving away from the discovery process and towards characterization, where follow-up observations of exoplanets are conducted to learn more about their atmospheres and environments.
In the process, exoplanet researchers hope to see if any of these planets possess the necessary ingredients for life as we know it. Recently, a pair of researchers from Northern Arizona University, with support from the NASA Astrobiology Institute’s Virtual Planetary Laboratory (VPL), developed a technique for finding oceans on exoplanets. The ability to find water on other planets, a key ingredient in life on Earth, will go a long way towards finding extraterrestrial life.
It seems unlikely that an ocean could persist on a world that never gets closer than 30 astronomical units from the Sun. But that’s the case with Pluto. Evidence shows that it has a sub-surface ocean between 100 to 180 km thick, at the boundary between the core and the mantle. Other Kuiper Belt Objects may be similar.
But time might be running out for these buried oceans, which will one day turn to ice.
We’ve found thousands and thousands of exoplanets now. And spacecraft like TESS will likely find thousands and thousands more of them. But most exoplanets are gassy giants, molten hell-holes, or frozen wastes. How can we find those needles-in-the-haystack habitable worlds that may be out there? How can we narrow our search?
Well, first of all, we need to find water. Oceans, preferably, since that’s where life began on Earth. And according to a new study, those oceans need to circulate in particular ways to support life.
Evidence from an ancient section of the Earth’s crust suggest that Earth was once a water-world, some three billion years ago. If true, it’ll mean scientists need to reconsider some thinking around exoplanets and habitability. They’ll also need to reconsider their understanding of how life began on our planet.
Between the scientific community, governments, humanitarian organizations, and even military planners, climate change is considered to be the single greatest threat facing humanity today. Between the increases in famine, disease, flooding, displacement, extreme weather, and chaos that result, it is clear that the way we are causing our planet to get warmer is having dire consequences.
But there a number of scenarios where the harm being done now could result in a runaway effect leading to mass extinctions. This possibility was illustrated in a recent study conducted by MIT professor Daniel Rothman with the support of NASA and the National Science Foundation (NSF). According to Rothman, we are in danger of breaching a “carbon threshold” that could lead to a runaway effect with Earth’s oceans.
Where did all of our water come from? What might seem like a simple question has challenged and intrigued planetary scientists for decades. So results just released by Rosetta mission scientists have been much anticipated and the observations of the Rosetta spacecraft instruments are telling us to look elsewhere. The water of comet 67P/Churyumov-Gerasimenko does not resemble Earth’s water.
Because the Earth was extremely hot early in its formation, scientists believe that Earth’s original water should have boiled away like that from a boiling kettle. Prevailing theories have considered two sources for a later delivery of water to the surface of the Earth once conditions had cooled. One is comets and the other is asteroids. Surely some water arrived from both sources, but the question has been which one is the predominant source.
There are two areas of our Solar System in which comets formed about 4.6 billion years ago. One is the Oort cloud far beyond Pluto. Everything points to Comet 67P’s origins being the other birthplace of comets – the Kuiper Belt in the region of Neptune and Pluto. The Rosetta results are ruling out Kuiper Belt comets as a source of Earth’s water. Previous observations of Oort cloud comets, such as Hyakutake and Hale-Bopp, have shown that they also do not have Earth-like water. So planetary scientists must reconsider their models with weight being given to the other possible source – asteroids.
The question of the source of Earth’s water has been tackled by Earth-based instruments and several probes which rendezvous with comets. In 1986, the first flyby of a comet – Comet 1P/Halley, an Oort cloud comet – revealed that its water was not like the water on Earth. How the water from these comets –Halley’s and now 67P – differs from Earth’s is in the ratio of the two types of hydrogen atoms that make up the water molecule.
Measurements by spectrometers revealed how much Deuterium – a heavier form of the Hydrogen atom – existed in relation to the most common type of Hydrogen in these comets. This ratio, designated as D/H, is about 1 in 6000 in Earth’s ocean water. For the vast majority of comets, remote or in-situ measurements have found a ratio that is higher which does not support the assertion that comets delivered water to the early Earth surface, at least not much of it.
Most recently, Hershel space telescope observations of comet Hartley 2 (103P/Hartley) caused a stir in the debate of the source of Earth’s water. The spectral measurements of the comet’s light revealed a D/H ratio just like Earth’s water. But now the Hershel observation has become more of an exception because of Rosetta’s latest measurements.
The new measurements of 67P were made by the ROSINA Double Focusing Mass Spectrometer (DFMS) on board Rosetta. Unlike remote observations using light which are less accurate, Rosetta was able to accurately measure the quantities of Deuterium and common Hydrogen surrounding the comet. Scientists could then simply determine a ratio. The results are reported in the paper “67P/Churyumov-Gerasimenko, a Jupiter Family Comet with a high D/H ratio” by K. Altwegg, et al., published in the 10 December 2014 issue of Science.
The ROSINA instrument observations determined a ratio of 5.3 ± 0.7 × 10-4, which is approximately 3 times the ratio of D/H for Earth’s water. These results do not exclude comets as a source of terrestrial water but they do redirect scientists to consider asteroids as the predominant source. While asteroids have much lower water content compared with comets, asteroids, and their smaller versions, meteoroids, are more numerous than comets. Every meteor/falling star that we see burning up in our atmosphere delivers a myriad of compounds, including water, to Earth. Early on, the onslaught of meteoroids and asteroids impacting Earth was far greater. Consequently, the small quantities of water added delivered by each could add up to what now lies in the oceans, lakes, streams, and even our bodies.
The Earth is often compared to a majestic blue marble, especially by those privileged few who have gazed upon it from orbit. This is due to the prevalence of water on the planet’s surface. While water itself is not blue, water gives off blue light upon reflection.
For those of us confined to living on the surface, the fact that our world is mostly covered in water is a well known fact. But how much of our planet is made up of water, exactly? Like most facts pertaining to our world, the answer is a little more complicated than you might think, and takes into account a number of different qualifications.
Sources of Water:
In simplest terms, water makes up about 71% of the Earth’s surface, while the other 29% consists of continents and islands. To break the numbers down, 96.5% of all the Earth’s water is contained within the oceans as salt water, while the remaining 3.5% is freshwater lakes and frozen water locked up in glaciers and the polar ice caps.
Of that fresh water, almost all of it takes the form of ice: 69% of it, to be exact. If you could melt all that ice, and the Earth’s surface was perfectly smooth, the sea levels would rise to an altitude of 2.7 km.
Aside from the water that exists in ice form, there is also the staggering amount of water that exists beneath the Earth’s surface. If you were to gather all the Earth’s fresh water together as a single mass (as shown in the image above) it is estimated that it would measure some 1,386 million cubic kilometers (km3) in volume.
Meanwhile, the amount of water that exists as groundwater, rivers, lakes, and streams would constitute just over 10.6 million km3, which works out to a little over 0.7%. Seen in this context, the limited and precious nature of freshwater becomes truly clear.
Volume vs. Mass:
But how much of Earth is water – i.e. how much water contributes to the actual mass of the planet? This includes not just the surface of the Earth, but inside as well. In terms of volume, all of the water on Earth works out to about 1.386 billion cubic kilometers (km³) or 332.5 million cubic miles (mi³) of space.
But in terms of mas, scientists calculate that the oceans on Earth weight about 1.35 x 1018 metric tonnes (1.488 x 1018 US tons), which is the equivalent of 1.35 billion trillion kg, or 2976 trillion trillion pounds. This is just 1/4400 the total mass of the Earth, which means that while the oceans cover 71% of the Earth’s surface, they only account for 0.02% of our planet’s total mass.
Source of Earth’s Water:
The origin of water on the Earth’s surface, as well as the fact that it has more water than any other rocky planet in the Solar System, are two of long-standing mysteries concerning our planet. Not that long ago, it was believed that our planet formed dry some 4.6 billion years ago, with high-energy impacts creating a molten surface on the infant Earth.
According to this theory, water was brought to the world’s oceans thanks to icy comets, trans-Neptunian objects or water-rich meteoroids (protoplanets) from the outer reaches of the main asteroid belt colliding with the Earth.
However, more recent research conducted by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, has pushed the date of these origins back further. According to this new study, the world’s oceans also date back 4.6 billion years, when all the worlds of the inner Solar System were still forming.
This conclusion was reached by examining meteorites thought to have formed at different times in the history of the Solar System. Carbonaceous chondrite, the oldest meteorites that have been dated to the very earliest days of the Solar System, were found to have the same chemistry as those originating from protoplanets like Vesta. This includes a significance presence of water.
These meteorites are dated to the same epoch in which water was believed to have formed on Earth – some 11 million years after the formation of the Solar System. In short, it now appears that meteorites were depositing water on Earth in its earliest days.
While not ruling out the possibility that some of the water that covers 71 percent of Earth today may have arrived later, these findings suggest that there was enough already here for life to have begun earlier than thought.
Anyone who lives close to ocean is familiar with the tides. And you probably know they have something to do with the Moon. But how do the tides work? Do other planets experience tides?
Just what the heck are tides? Some kind of orbit jiggle jello effect from the magic Etruscan space-whale song? Is it an unending slap-back of gravitometric Malthusian resonance originating from the core of the Sun’s crystalline liver-light organelles? Is it all the plankton agreeing to paddle in the same direction at their monthly oceanic conferences?
As certain as I am that you enjoy my word terminology salads, with apologies to Papa Bear, we both know tides are caused by the gravitational interaction with the Moon. You would think we’d have only one high tide and one low tide, with the Moon pulling the Earth’s water towards it. Moon goes one side, water rushes over to that side, moon goes to other side, water chases around to follow it. But the tides make the water levels appear to rise twice a day, and lower twice a day in 6 hour increments. So, it’s clearly more complicated than that.
The gravity from the Moon does pull the water towards it. That’s what gives you the highest tide of the day. It’s a bulge of water that follows the Moon around and around as the Earth rotates. This makes sense to us. But then Earth itself is pulled with a little less gravity than the water towards the Moon and, the water on the opposite side of the Earth is pulled with even less gravity, and so you wind up with another bulge on the opposite side of the Earth.
So from our perspective, you end up with a bulge of water towards the Moon, and a bulge away from it. The part of the Earth with the water getting pulled towards the Moon experiences a high tide, and same with the part on the opposite side of the Earth with the other bulge. Correspondingly, the parts of the Earth at right angles are experiencing low tides.
It would be hard enough to predict with a simple spherical Earth covered entirely by water, but we’ve got continents and coastlines, and that makes things even more complicated. The levels that the tides rise and fall depend quite a bit on how easily the water can move around in a region. That’s why you can get such big tides in places like the Bay of Fundy in Canada.
Our Sun also contributes to the tides. Surprisingly, it accounts for about 30% of the them. So when the Sun and the Moon are lined up in the sky, you get the highest high tides and the lowest low tides – these are Spring Tides. And then when the Sun and Moon are at right angles, you get the lowest high tides and the highest low tides. These are Neap Tides.
Tidal forces can be very powerful. They can tear galaxies apart and cause moons to get shredded into pieces. Perhaps the most dramatic example is how Jupiter’s enormous gravity pulls on Io so strongly that its surface rises and falls by 100 meters. This is 5 times greater than the Earth’s biggest water tides. This constant rise and fall heats up the moon, giving it non-stop volcanism.
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