Month: September 2019

Interstellar Comet Borisov Looks Weirdly Familiar

The gas cyanogen has been detected in 2I/Borisov’s coma—a historic detection of a gas commonly found in regular comets.

Artist’s impression of a cometary nucleus. [ESA]

It’s official, the solar system is playing host to its second confirmed interstellar visitor only two years after the strangely-shaped `Oumuamua was spotted receding into interstellar expanse. While `Oumuamua was historic in that it was the first confirmed interstellar comet to be discovered, according to a new study (which has yet to be peer reviewed), this newest interstellar vagabond is potentially more significant:

“For the first time we are able to accurately measure what an interstellar visitor is made of, and compare it with our own solar system,” said Alan Fitzsimmons of the Astrophysics Research Center, Queen’s University Belfast, in a statement.

So, why are astronomers so excited about 2I/Borisov?

A (Cometary) Star Is Born

In late August, the comet was discovered by Gennady Borisov, an amateur astronomer in Crimea, and initially designated “C/2019 Q4” because, well, it looked like a regular comet. It was only after repeated observations by Borisov, and confirmed by other amateur and professional astronomers, that the object’s path and speed through the solar system could be realized. It turned out to be traveling fast.

Like, really, really fast.

Clocked at a breakneck pace of 93,000 miles per hour (150,000 kilometers per hour), astronomers realized that C/2019 Q4 was a special kind of comet. While it was found to possess the characteristics of a regular comet (it has a faint coma and tail) there is no way that it’s gravitationally bound to our Sun. Its trajectory is hyperbolic. In other words, it didn’t originate in our solar system—it’s an alien visitor.

This simple animation depicts the comets path through our neighborhood; there’s little ambiguity in the fact that it doesn’t intend to hang around for very long:

With only a slight tug by our Sun’s gravity, the interstellar visit will careen out of the solar system in a few months. [NASA/JPL-Caltech]

Last week, these factors all culminated in the International Astronomical Union (IAU) officially classifying C/2019 Q4 as the second unambiguous interstellar comet discovery to date. It was therefore reclassified as “2I/Borisov” (1I/`Oumuamua being the first, of course). It’s thought interstellar junk passes through our solar system all the time, but only two comets (to date) have been confirmed to have an interstellar origin, suggesting our observational techniques are improving.

Now, the really neat thing about 2I/Borisov is that it’s a lot more active than `Oumuamua; the latter produced very little in the way of a discernible coma or tail after its discovery. Borisov, however, is being far more generous, already allowing astronomers to grab a crude spectroscopic snapshot of the gases being vented into space.

A Mysterious Interstellar Time Capsule

After being thwarted by the glare of the Sun on Sept. 13, an international team of astronomers was able to use the William Herschel Telescope on La Palma in the Canary Islands in the morning of Sept. 20 to measure the light that was being scattered off the gases in its tenuous coma. Follow-up spectral analysis by the TRAPPIST-North telescope in Morocco was also used.

Measuring the spectrum of Borisov allows us to understand the chemical composition of the ices that are fizzing into space as they are slightly heated by our Sun’s radiation via a process known as sublimation. And this is profoundly awesome.

To capture the spectra of any comet reveals the chemicals it contained when it formed billions of years ago. In our solar system, comets are considered to be icy time capsules; they formed from the solar nebula when the Sun was a proto-star and the planets were just starting to accrete from the surrounding protoplanetary disk of ancient debris. To see the chemicals contained within the vapor of these fizzing “dirty snowballs” gives us a five-billion-year-old glimpse of what the solar nebula and its system of baby planets would have contained.

2I/Borisov as imaged by the Gemini North Telescope on Hawaii. [GEMINI OBSERVATORY/NSF/AURA/INTERNATIONAL ASTRONOMICAL UNION]

Borisov wasn’t formed in our solar nebula, however, it was formed from the nebula of a distant, unknown star of unknown age. We have little idea as to where or when it originated (though there’s little doubt that astronomers will use data from the European Gaia space telescope to try to figure out a rough estimate, as they did with `Oumuamua).

Surprisingly Familiar

While previous observations of the comet’s nucleus have revealed a reddish tinge that is similar to the long-period comets that originate from our solar system’s Oort Cloud (such as Hale-Bopp and Hyakutake), the new study has been able to identify another familiar trait: its venting gases contain cyanogen. This chemical is a simple, yet toxic molecule containing one carbon atom and a nitrogen atom (CN). Cyanogen is commonly found in regular comets born in the solar system.

The researchers were also able to make an estimate of the ratio of the dust to gas that is being blasted from the comet’s nucleus and, you guessed it, it is roughly in agreement to what you’d expect a regular comet to generate.

All of these findings point to an unexpected conclusion, as the researchers highlight in their paper: “If it were not for its interstellar nature, our current data shows that 2I/Borisov would appear as a rather unremarkable comet in terms of activity and coma composition.” In other words, if it wasn’t for its extreme speed, 2I/Borisev would look like a regular comet from our solar system.

Does this mean all comets from any star system have similar compositions? That doesn’t seem possible, considering we know other stars and their associated nebulae their comets would have formed from contain different chemicals to our own. It could just mean that Comet Borisov was ejected from a nearby star that formed in the same stellar nursery as our Sun five billion years ago and should therefore contain approximately the same chemicals. But for now, it’s too early to say.

Obviously, more work needs to be done and, fortunately, we have time. The comet will reach perihelion (point of closest approach to the Sun) in early December, and astronomers are predicting maximum nucleus activity in December and January before it starts to recede into the interstellar night.

So, watch this space.

The Sun Is a Beautifully Blank Billiard Ball for Halloween

For the festive season, our nearest star is keeping its choice of costume simple.

I’m not saying the Sun isn’t being creative, it’s just not putting too much effort into this year’s stellar fancy dress party. I mean, look at it:

The Sun right now, as seen by the Helioseismic and Magnetic Imager (HMI) instrument on NASA’s Solar Dynamics Observatory (SDO) [NASA/SDO]

That flawless orange billiard ball is the photosphere of our Sun. Have you ever seen something so smooth and beautifully unremarkable?

Well, you have now, and its blank gaze is actually the reason why it’s causing a bit of a stir. According to our ever watchful solar sentry, Tony Phillips at SpaceWeather.com, the northern summer of 2019 may go down in history as “the summer without sunspots.”

From June 21st until Sept 22nd, the sun was blank more than 89% of the time. During the entire season only 6 tiny sunspots briefly appeared, often fading so quickly that readers would complain to Spaceweather.com, “you’ve labeled a sunspot that doesn’t exist!” (No, it just disappeared.) Not a single significant solar flare was detected during this period of extreme quiet.

Dr. Tony Phillips

So, what does this mean?

Sunspots are the visual cues for magnetic turmoil within our nearest star. Over cycles of approximately 11 years, the Sun’s internal magnetic field becomes stretched and twisted, driving the ebb and flow of space weather.

Starting with our solar billiard ball here, suffice to say that the solar magnetic field is pretty untwisted and, well, chilled. This is the epitome of “solar minimum” — and, as commented on by Phillips, a deep, potentially record-breaking solar minimum at that. It’s very likely that this is as minimum as solar minimum can be, so we could hazard a guess to say that things are going to start getting interesting very soon.

Differential rotation and the formation of coronal loops as demonstrated by my awesome abilities as a Microsoft Word artist [source: my PhD thesis!]

As our Sun is a massive blob of magnetized plasma, it doesn’t rotate uniformly (like the Earth does), it actually rotates a little faster at its equator than at its poles, a phenomenon known as “differential rotation.” Now, if you imagine the solar magnetic field as straight lines running from pole to pole, you can imagine that, over time, the field will start to wrap around the equator like an elastic band being stretched out of shape and wrapped around the middle. At its most extreme, so much rotational tension will be applied to the magnetic field that it becomes contorted. This contortion creates an upward pressure, forcing vast loops of magnetized plasma, known as coronal loops, to pop through the Sun’s photosphere — a.k.a. the solar “surface” — like annoyingly twisted loops of garden hosepipe (see the diagram above).

As its most extreme, in a few years time, we can expect our boring ol’ billiard ball to look something like this:

The Sun in 2014 (during the previous solar maximum), as seen by the SDO’s HMI [NASA/SDO]

About those blotches: those dark spots are sunspots and they are a direct consequence of the magnetic turmoil that rumbles inside the Sun during solar maximum. Remember those coronal loops I was talking about? Well, these huge, beautiful arcs of plasma cause the hotter outer layers of the Sun to be pushed aside, exposing the comparatively cooler (though still thousands of degrees) plasma under the surface — that’s what creates those dark blotches. And by counting sunspots, you can gauge how magnetically active the Sun is.

By viewing the Sun in different wavelengths, we can view the Sun’s atmosphere at different temperatures and, as the Sun’s atmosphere (the corona) is counter-intuitively hotter the higher above the surface you get, let’s take a look at what solar maximum looks like above these sunspots:

Yikes! The Sun’s corona in October 2014 (during the previous solar maximum), as seen by the SDO’s Atmospheric Imaging Assembly (AIA) instrument. And a damn fine effort just in time for Halloween. [NASA/SDO]

As you can see, there’s a lot of coronal loops erupting through the surface, creating huge regions of activity (called active regions, unsurprisingly). And the above observation was captured on Oct. 8, 2014, when the Sun was, apparently, in a terrifyingly festive Halloween mood! These regions can be hothouses for solar flares and coronal mass ejections; explosive phenomena that can have dramatic space weather effects on Earth.

So that was solar maximum; what does the solar corona look like now, at solar minimum?

The Sun’s corona right now, as seen by the SDO’s AIA [NASA/SDO]

Yep, as you guessed, very relaxed. In this state, we can expect very little in the way of explosive space weather events, such as flares and CMEs; there’s simply too little magnetic energy at solar minimum to create many surprises (caveat: even solar minimum can generate flares, they’re just few and far between).

While the Sun may look boring, the effects of space weather are anything but. During these times of solar minimum, the extended solar magnetic field (called the heliosphere), a magnetic bubble that reaches beyond the orbits of all the planets, contracts and weakens, allowing more cosmic rays from energetic events from the rest of the cosmos to reach Earth. Cosmic rays are ionizing particles that can boost the radiation exposure of astronauts and frequent fliers. Also, the solar wind can become a more persistent presence; streams of energized particles that are continuously streaming from the lower corona, so we still get our aurorae at high latitudes.

Recognition that the Sun is now in a deep minimum means the solar vacation is nearing an end. Astronomers have reported that of the handful of sunspots have made an appearance over the last few months with a flip in magnetic polarity, which can mean only one thing: Solar Cycle 25 is coming and the next solar maximum is only four years away.

SCIENCED Podcast: No Tea on Teegarden b

Are you sure it’s THAT habitable? [NASA]

Before zipping off to Hawaii and taking a short writing break, I was invited to appear on the SoCal Science Writing “SCIENCED” podcast with Jessie Hendricks to talk about one of our favorite habitable exoplanets, Teegarden b. So, naturally, we trashed its potential habitability with some science and humor. We also delved into some science communication, how I became a space writer, the search for extraterrestrials, and the meaning of life itself. It’s a fun discussion and Jessie is a fantastic host, check it out.

Are you a science writer/communicator in Southern California? Join the SoCal Science Writing association!