Monday, February 01, 2016

rogue planet and star linked

Saw a blurb on Facebook from Wired about a huge solar system discovery. I was intrigued.

That link landed me at the science article at the web site. Their title: Scientists Just Discovered a Solar System Larger Than Our Own — Much Larger. They talked about a potentially huge solar system discovered by Dr Deacon. However, I found the article strange in a couple of ways. And the more I thought about it, the more it bugged me.

It seemed to me they emphasised the Earth-Sun distance. Sure, OK, to help make it a bit more relatable. But the proper way to compare the size of other star systems to our solar system is not with Earth! If nothing else, use Neptune. Or Pluto. If you're going to compare apples, you don't compare an apple to the seed of the other. Heck. Maybe they could make a comparison to solar system sizes in light of the rumoured Planet 9, which might be the new dimension-setting parameter for our system!

Let's do the math.

The article says that planet 2MASS J2126 is 1 trillion kilometres away from its possible home star TYC 9486-927-1. And they say this is 7000 times the Earth-Sun distance.

I am assuming 2MASS J2126 is one exoplanet of possibly others orbiting TYC 9486-927-1. And I am assuming 2MASS J2126 is the outer-most exoplanet in that system.

The Earth-Sun distance is around 150 million km. Let's use 149 600 000 km for our calculations. 1 trillion divided by our distance from the Sun is: 6684. Around 6700. Not 7000. But close enough. My concern however is that others looking at this will not appreciate the subtlety. If it is the outer-most exoplanet then the 2MASS J2126's system is not 7000 times bigger than our solar system.

Let's take Neptune as the defined outer limit to our solar system. It is 4 497 000 000 km from the Sun. I.e. 4.5 billion. Compared to 1 trillion. That means the 2MASS J2126 system is 222 times larger. That's a far cry from 7000.

What about Planet 9? If it truly exists and is where they think it is, let's consider it the outer edge of our solar system. Planet 9 is thought to be somewhere around 20 times the distance of Neptune from the Sun. I.e. 90 billion km, roughly. And that then makes the 2MASS J2126 system merely 11 times larger than ours. Merely! That's still huge.

I came away from the web site feeling that they were distorting things. Not really presenting the facts in as clear a way as possible. I hate when people mess up the numbers.

Hello. Use an infographic!

graphic showing comparative sizes of planet orbits

Viewed this way, you can see that an Earth-orbit to 2MASS J2126-orbit is a bit ridiculous. You can't even see Jupiter and Saturn at this scale!

Consequently, I missed something when I moved on to the RAS article. Guess I was in a tiff at that point. But upon review, the tone, the thrust of that piece is very different. It's title: 1 trillion kilometres apart: a lonely planet and its distant star. It shows that Deacon is studying a number of "wide" systems and rogue planets. A key point of the paper is the measurement of the planet and star vectors and showing how they match. And the reference here, to 7000, is to simply allude to the Astronomical Unit. Simply put: 2MASS J2126 is 7000 AU from its star.

There's an easy-to-relate-to option!

bodydistance from star in AU
Pluto between 30 and 49
Planet 9600
2MASS J21267000

Take the article with a grain of salt. I think they are trying to sex-up the content. Make it sensational. is a news site for millennials. The RAS article, not surprisingly, is about the science. And it's fascinating.


Nicole made an interesting statement to me. What if 2MASS J2126 is the inner-most exoplanet in this system, analogous to Mercury. Wow... Now that's huge.

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