Category: solar system

Goodbye ‘Oumuamua, Hello Borisov; This Is What Two Interstellar Interlopers Can Teach Us

“The most interesting aspect of what we know so far about interstellar objects is how different the first two, ‘Oumuamua and Borisov, truly are from one another. There are a number of ways to form interstellar bodies: from failed star systems in star-forming regions, from ejected asteroids, from comets, and from collisional debris. We do not know how common or rare objects of all these different types are, nor how to definitively classify the ones we’ve seen so far, but hope is on the way. Beginning in the 2020s, the Large Synoptic Survey Telescope will come online, expected to uncover dozens of such objects by 2030.

What are the size and frequency distributions of the interstellar population? How old and/or weathered are they? Are they comet-like or asteroid like; volatile-rich or volatile-free, and do different classes of object originate from different regions in the sky? Are most small objects inactive while most large ones are active? With the tip of the interstellar iceberg uncovered, the answers to these questions and more are at last within our reach.”

In our solar system, asteroids, centaurs, comets, Kuiper belt and Oort cloud objects all have their own unique story, but possess many qualities common to each separate class. Occasionally, one of these objects will get ejected, where it will wander the Milky Way indefinitely, until it encounters another object.

Back in our Solar System, we’ve begun discovering and identifying objects in our neighborhood that originated from interstellar space. In 2017, ‘Oumuamua became the first, and it was extremely odd: small, elongated, and already on its way out. Our picture is now changing dramatically, as a second interstellar object, 2I/Borisov, was just discovered.

With its closest approach coming in early December, astronomers worldwide are getting ready. Here’s what we know so far.

Saturn, Not Earth Or Jupiter, Has The Largest Storms In Our Solar System

“But from December of 2010 to August of 2011, the largest storm of all occurred: on Saturn. For 200+ days, this Saturnian hurricane raged, maintaining its leading “head” until May. It came to encircle the entire planet, as methane-poor tail end stands out against the relatively methane-rich remainder. Viewed 11 hours (1 Saturn-day) apart, we determined the hurricane migrated across Saturn at 60 miles-per-hour (100 kph). These storms have occurred every 20-30 years since first observed in 1876, as hot air rises, cools and falls.”

Many worlds in our Solar System have enormous storms that occur in their atmospheres. Earth routinely experiences hurricanes, with wind speeds frequently in excess of 225 kph. But what happens on the giant worlds in our Solar System dwarf anything that happens on Earth. Saturn’s hurricane at its north pole is bigger and faster than any hurricane we’ve ever seen here. Jupiter’s great red spot is bigger than the entire Earth itself. But the largest storm of all? 

Believe it or not, it’s a periodic weather event that appears to occur on Saturn every 20-30 years or so. Keep your eyes peeled in the 2030s, because it’s going to return!

Why Does Jupiter Get Hit By So Many Objects In Space?

“Yes, Jupiter is bigger than Earth, and that enhanced size accounts for a little over a factor of 100 in collision frequencies. But realistically, collisions on Jupiter are even hundreds of times more frequent than that. Why? Because Jupiter’s gravitational pull is sufficient to attract huge numbers of comets and asteroids that come too close to it, in a way that Earth cannot. Jupiter is struck so frequently due to a combination of gravity and the fact that objects farther from the Sun — even fast-moving comets — have slower velocities, and are therefore easier to capture.

Size does matter, but not as much as gravity does. In particular, not as much as gravity does relative to the speeds that objects near this gas giant move at. The only object in the Solar System better at capturing asteroids and comets is the Sun, but Jupiter is a very strong #2! Jupiter, contrary to popular belief, doesn’t appear to protect the inner Solar System very much at all, but rather serves as a tremendously good punching bag for objects that, otherwise, wouldn’t strike anything at all.”

Jupiter has been called the shield of the Solar System. We have this longstanding idea that Jupiter protects the Earth from asteroid and comet strikes, and that without its influence, we’d be struck by a catastrophic impact more often than we are with it around. Why do scientists think that? Is it true? And why, over the past 3 decades, have we seen so many large impacts on Jupiter?

That last question, at least, is one that scientists know the answer to. Come get the full story on Jupiter’s bombardment today!

Yes, Two Planets Can Both Share The Same Orbit

“It’s no surprise that planetary orbits might also obey an orbit-swapping resonance, with Janus and Epimethius providing a spectacular example. You might object that these are moons around a planet, not planets around a star, but gravity is gravity, mass is mass, and orbits are orbits. The exact magnitude is the only difference, while the dynamics can be extremely similar.

Considering that we now know of exoplanetary systems that exist in great abundance around M-class, red dwarf stars, and that they appear analogous to either the Jovian or Saturnian systems, In other words, it’s totally conceivable that we’d have a planetary system somewhere in our galaxy with two planets (rather than moons) that do exactly this!”

Have you ever wondered whether two planets could potentially share the same orbit? I don’t mean temporarily: I mean indefinitely, such as for billions of years, lasting in the same orbit for as long as their parent star shall ever live?

It turns out that not only is it possible, but we’ve got an example in our Solar System that demonstrates exactly how it could happen. So, so cool.

Starts With A Bang Podcast #47 – Ice Giants At The Solar System’s Edge

What do we really know, and what mysteries are left to solve, about the outer worlds of our Solar System, and about the gas giant and ice giant worlds found throughout the Universe? Remarkably, if you had asked this same question 30 years ago, we would have had a quaint story about how planets form and why our Solar System has the planets it does, and we assumed that these rules would be extended to all solar systems in the galaxy and Universe. But with the deluge of exoplanet data, accompanied by better observations and simulations of our Solar System, that old story isn’t even the half of it.

I’m so lucky to get to interview Heidi Hammel for this edition of the podcast, who, as a bonus, was the lead investigator on the Hubble Space telescope when Comet Shoemaker-Levy 9 impacted Jupiter back in 1994! Come listen to one of my favorite interviews ever today!

(Image credit: NASA/Voyager 2)

This Is Everything That’s Wrong With Our Definition Of ‘Planet’

“There are many people who would love to see Pluto regain its planetary status, and there’s a part of me that grew up with planetary Pluto that’s extraordinarily sympathetic to that perspective. But including Pluto as a planet necessarily results in a Solar System with far more than nine planets. Pluto is only the 8th largest non-planet in our Solar System, and is clearly a larger-than-average but otherwise typical member of the Kuiper belt. It will never be the 9th planet again.

But that’s not necessarily a bad thing. We may be headed towards a world where astronomers and planetary scientists work with very different definitions of what attains planethood, but we all study the same objects in the same Universe. Whatever we call objects — however we choose to classify them — makes them no less interesting or worthy of study. The cosmos simply exists as it is. It’s up to the very human endeavor of science to make sense of it all.”

Next month will mark 13 years since the International Astronomical Union (IAU) officially defined the term planet and ‘Plutoed’ our Solar System’s (up-until-that-point) 9th planet. With an additional 13 years of knowledge, understanding, data, and discoveries, though, did they get the decision right?

Certainly, there were aspects that needed to be revised, but the IAU’s definition comes along with some major gaps and mistakes. We can do better! Come learn how.

What Was It Like When Venus And Mars Became Uninhabitable Planets?

“But the changes that Mars endured were rapid and sweeping. Planets are born with a fixed amount of internal heat, which radiates away over their lifetime. A planet like Mars, with half the diameter of Earth, is born with only about 10-15% the amount of internal heat as our world, and will therefore see a greater percentage of it radiate away much faster than Earth will.

Approximately 3 billion years ago, the core of Mars became cool enough that it stopped producing that protective magnetic dynamo, and the solar wind began striking the Martian atmosphere. In short order, which is to say in just tens of millions of years, the atmosphere was knocked off into interplanetary space. As a result, the oceans were unable to remain in liquid form, and either froze beneath the surface or sublimated away.”

When our Solar System first formed, it wasn’t just Earth that looked promising for life, but also Venus and Mars. All three of these planets had large, liquid water oceans, substantial atmospheres, and the ingredients for complex biochemistry and even life. Over on Venus, its close proximity to the Sun and the large presence of atmospheric water vapor led to a runaway greenhouse effect, boiling the oceans after just ~200 million years. But Mars, despite being small and distant, maintained Earth-like conditions for 1.5 billion years. Considering that life arose on Earth after just one-sixth of that duration, perhaps Mars once had life, too?

Come get the story of the Solar System’s closest version of a failed version of Earth, Mars, and learn how it ultimately lost its chance at habitability.

What Was It Like When Planet Earth Took Shape?

“There was almost certainly a high-energy collision with a foreign, out-of-orbit object that struck our young Earth in the early stages of the Solar System, and that collision was required to give rise to our Moon. But it was very likely much smaller than Mars-sized, and it was almost certainly a sturdy strike, rather than a glancing collision. Instead of a cloud of rock fragments, the structure that formed was a new type of extended, vaporized disk known as a synestia. And over time, it settled down to form our Earth and Moon as we know them today.

At the end of the early stages of our Solar System, it was as promising as it could be for life. With a central star, three atmosphere-rich rocky worlds, the raw ingredients for life, and with gas giants only existing much further beyond, all the pieces were in place. We know we got lucky for humans to arise. But with this new understanding, we also think the possibility for life like us has happened millions of times before all throughout the Milky Way.”

One of the deepest existential questions we can ask about the Universe is how, after more than 9 billion years, all the phenomena in our cosmic history led to the creation of planet Earth. Going from an environment where stars were actively forming to one where the Sun, Earth, and all the other planets were in place is a daunting task for people who create scientific simulations of our early environment, and involves gravitational interactions, planetary migrations and ejections, and even enormously energetic collisions between planets and proto-planets.

Yet somehow, it all came together, and gave rise to us. From what we’re learning, we might not even be all that rare. Come check out the current story.

What Was It Like When Our Solar System First Formed?

“Over the past few years, we’ve finally been able to observe solar systems in these very early stages of formation, finding central stars and proto-stars shrouded by gas, dust, and protoplanetary disks with gaps in them. These are the seeds of what will become giant and rocky planets, leading to full-on solar systems like our own. Although most of the stars that form — including, very likely our own — will have formed amidst thousands of others in massive star clusters, there are a few outliers that form in relative isolation.

Although the history of the Universe may subsequently separate us from all of our stellar and planetary siblings from the nebula that they formed in billions of years ago, scattering them across the galaxy, our shared history remains. Whenever we find a star with approximately the same age and abundance of heavy elements as our Sun, we cannot help but wonder: is this one of our long-lost siblings? The galaxy is likely full of them.”

It took a whopping 9.2 billion years of cosmic evolution for the Universe to give rise to the very beginning of our Solar System; our Sun and planets didn’t form until 2/3rds of the time since the Big Bang had passed. In order to get there, we needed to form the right ingredients for life, rocky planets, and the chemistry we need. But when it happened to us, we weren’t alone. It likely happened exactly the same way for thousands of other stars at once, and continues to happen even up through the present day.

Are we alone in the Universe? The cosmic story that brought us to existence seems to be a story that’s universal. Here’s a key step in how we got here.

A Billion Years In Interstellar Space: What We Know Today About ‘Oumuamua

“The incredible conclusion isn’t just that ‘Oumuamua came from outside
of our Solar System, but that this was both rare and common. For an
individual object, like ‘Oumuamua, it will likely never come this close
to another Solar System again. Only once every 100 trillion years — some
10,000 times the current age of the Universe — will it pass so close to
a star. As scientist Gregory Laughlin put it, “this was the time of
‘Oumuamua’s life.”

But for our Solar System, because of the sheer
number of objects like this flying through the galaxy, we probably
experience a close encounter like this around a few times per year. 2017
marked the first time we saw such an object, but we’ve likely gotten
billions of them over the course of our Solar System’s lifetime. Some of
them, if nature was kind, may have even collided with Earth.

There may be as many as ~1025
of objects like this flying through our galaxy, and every so often,
we’ll get lucky enough to encounter one of them. For the first time,
we’ve actually seen one of them for ourselves.”

In 2017, our Solar System received a visit like never before: from an object originating from interstellar space. Likely ejected more than a billion years ago from a foreign solar system, it happened to pass within even the orbit of Mercury, only becoming visible to our telescopes when it came within 60 lunar distances of the Earth.

But we found it, observed it, and learned everything we could about it. What do we know, today? Spoiler: it’s not from aliens.