“ Seen from about 6 billion kilometers, Earth appears as a tiny dot (the blueish-white speck approximately halfway down the brown band to the right) within the darkness of deep space
Pale Blue Dot by Carl Sagan
From this distant vantage point, the Earth might not seem of any particular interest. But for us, it’s different. Consider again that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.
The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we’ve ever known.
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Dust and the Helix Nebula ~ Dust makes this cosmic eye look red. The eerie Spitzer Space Telescope image shows infrared radiation from the well-studied Helix Nebula (NGC 7293) a mere 700 light-years away in the constellation Aquarius
Gas giants bully smaller planets into giving them pebbles.
Planets come in all shapes and sizes – but how do gas giants become so big, whilst other planets remain comparatively small? New research has suggested that planets such as Saturn and Jupiter – the gas giants – form relatively quickly by gathering up small, pebble-sized bits of matter before their smaller siblings can get to them.
In a young planetary system, a star forms from a collapsing cloud of rotating gas. This spinning cloud of gas is surrounded by dust, which clumps together over time under its own gravity. These ‘clumps’ eventually form pebbles, asteroids and planets, which then orbit the newly-formed star. Exactly how the planets form is still a question that remains to be answered.
Gas giants are massive planets composed of mostly hydrogen and helium, with a rocky core. The first stage in forming these planets is the production of this core. Previously, scientists believed that the cores are formed via the accretion of dust from the solar nebula clumping together to form large, rocky chunks, which collapse under their own gravity. Over time, they slowly attract more and more mass to form planetary embryos called planetesimals. Once these planetesimals are large enough, they attract nearby hydrogen and helium to form gas giants. However, this model does not explain why gas giants are so big and other planets aren’t so much. New observational evidence suggests that gas giants actually form quite quickly after the formation of the host star, and up to 1000 times faster than previously thought.
The key to this swift formation, and the discrepancy in planetary sizes, is in the pebbles. Once large enough, the different sized planetesimals will form their own orbit around the burgeoning star; the largest of these go on to form gas giants. The pebbles, with their smaller size, don’t have the same defined orbit as they are smaller and therefore more unstable. They get easily disturbed by passing objects, as well as by the gas and dust that still surrounds the growing star. If a massive object passes by, the pebbles are easily attracted by its gravity. They get drawn in and add to its mass. The larger planetesimals attract pebbles much more strongly than the smaller ones, so the infant gas giants acquire more and more mass, whilst the smaller planets don’t get a look in. Essentially, the future gas giants barge through the pebbly path, scooping up pebbles and clearing the way before the smaller planets get the chance.
This new model paves the way to understanding the formation of our own solar system, as well as other planetary systems that might be out there.
The Cassini mission around Saturn is winding down. Similarly, New Horizons and the Voyager missions will end in the near future. As sad as this is: we’re about to lose many of our missions in the outer solar system, due simply to age.
Missions like these will leave a large vacuum in the space community when they go.
NASA, it seems, agrees.
Jim Green, NASA’s head of planetary sciences, just requested NASA’s Jet Propulsion Laboratory to initiate a study on how to put a flagship-sized mission into orbit around Uranus and possibly Neptune too.
Paul Scott Anderson summarized well the subjects to be addressed by the mission:
Study origin and evolution of our Solar System – giant planet migration, with major complementarity with exoplanets
Investigate habitability of icy worlds – to gain insight into the origin of life on Earth
Understand the dynamic nature of processes in our Solar System – importance of time domain
Explore giant planet processes and properties
Use giant planets to further our understanding of other planets and extrasolar planetary systems
Determine giant planets’ influences on habitability
If this mission(s) are endorsed by scientists during the 2022 decadal survey then we’ll likely be sending at least one big spacecraft out to one of these two ice giants to live there for many years.
There’s much we don’t know about these worlds. Neptune for example has a moon (Triton) which orbits in retrograde meaning it came from somewhere else. Could it be debris from a collision in the early solar system? A captured rogue/exoplanet? Could it be habitable (it has cryovolcanoes)?
A wealth of exploration and discovery awaits us in the outer solar system. With this news it seems like we’re not about to abandon ourselves to the darkness of ignorance.