Massive rugby ball-shaped planet emerges from scrum of space 'scope sightings Just over 1,500 light-years away in the constellation of Hercules there’s a rugby ball-shaped exoplanet orbiting a star. It’s the first time astronomers have been able to detect such an unusual shape of an alien world. Most planets are more or less spherical due to gravitational forces that pull matter equally in from all …
How short is short? This observation could be within any ring lifetime.
Other possibilities could be a recent body break up due to tidal forces blocking light asymmetrically, which could also be a reason for the orbital disturbance, i.e. some sort of close pass in a chaotic gravitational environment.
Rings don't form quickly. When the body they come from breaks up it takes time for the rubble to spread out in an orbit to the point where you can call it a ring. If that happened in this scenario then the gravity of the star would be disruptive enough that the ring would never have time to form in the first place.
Plus the amount of sunlight the ring would block would be a fraction of the amount a bulge would block. This would change the data that was observed such that the extra sunlight blocked would probably have been hidden amongst the noise of the signal.
No. These observations are basically looking at the intensity of light coming from the star, and spotting how the intensity drops when a planet passes in front of it. Planetary rings are extremely diffuse collections of dust and small objects, and therefore won't block anywhere near as much light as the body of a planet. Seeing planets in this way has only become possible in the last couple of decades, and this is the first time someone has managed to get some idea of the shape of such a planet. Measuring things like rings and moons will need a few orders of magnitude more sensitivty, and so is likely at least a couple more decades away, if it becomes possible at all.
The Moon is moving farther away from the Earth because it is tidally locked, and is stealing rotational energy from the Earth (via tides) to move to higher orbits.
Even though this planet is a gas giant its rotaion may have been slowed to almost nothing by the tidal forces of the star, and is now stealing rotational energy from the star to move away from it.
The planet's rotation doesn't factor into it for those purposes; what matters is the parent body's rotation, i.e. the star's in this case. Given that the planet orbits in less than a day per the article, I'd be slightly surprised if the star rotated faster than that, as would be required for it to be enlarging/lengthening the planet's orbit (cf. the Earth rotates in rather less than a month, which is why it can boost the Moon's orbit around it), but I'm basing that on a sample size of one, knowing that the Sun rotates in about 26 days (depending on latitude).
I've added a data point; remembering Vega being fairly remarkable in its rotation, I looked up that that one does rotate in 12.5 hours, but its rotation is quite egregious, so it's possible but unlikely that this star does rotate fast enough for that to happen. Further checking on Wikipedia suggests that the planet's more precise orbital period is 0.926 days, and if I've done my sums right, the star's rotation period is just under a week, so that wouldn't work for an explanation. But it's definitely worth considering before eliminating it, indeed.
> the Earth rotates in rather less than a month
Well, the moon rotates around the earth in 27.32... days relative to the fixed stars: this is the sidereal month. I don't think the Earth rotates around anything in those timeframes (unless you're using a selenogical frame of reference, in which case, yuk!)
.... I told you before an I'll tell you again.
Stop looking at the sky with a dirty telescope lens and no spectacles on.
The only thing you'll find up in the sky is our god in heaven...
(and maybe a rugby ballish bit of stone)
God bless 'ya all, Mary. (PS Prayer meeting tonight cancelled due to Jumble Sale being double booked)
"The rocky part doesn’t move that much."
A foot (30 cm) or more vertical displacement is not insignificant, it can upset GPS calibrations and similar. It's only the fact that the period is so long (12 hours plus) and that everything moves together that we don't notice it.
I was about to have the same rant about solid earth tides. One of the groups they're hugely important to is....astronomers (using earth-based observatories to do detailed measurements).
I'm not sure if I'm being pedantic or misunderstanding the tidal forces... I'm assuming it's actually a very oblate spheroid making it look like a rugby ball from the side only?
Or... to be a rugby ball shape (prolate spheroid?), does that imply that the planet's rotational axis is at 90 degrees, similar to Uranus?
I think they're saying it's stretched out by tidal forces along one axis, pointing toward & away from the star, so yes, a prolate spheroid, but with a fairly conventional axis, presumable roughly perpendicular to the orbital plane. The oblate spheroids are explained by centrifugal/centripetal force, nothing tidal to that at all.
!!! SPOILER ALERT !!!
At the end of 'The Light Fantastic'* by Terry Pratchett, some 'planets' orbiting a star hatch into baby star turtles, each with their own tiny disc world and supporting elephants.
*Start with 'The Colour of Magic', as 'The Light Fantastic' starts off directly from the end of that book.
Hal Clement's classic 1954 book: A Mission of Gravity".
Set on a large planet spinning so fast it flattens out to look like an old style spinning top (days take minutes), such that the surface gravity varies hugely with latitude, which itself has all sorts of interesting consequences (eg, the sky+horizon looking inverted, bowl-shaped).
Recommended! A great hard-sf classic.
Nice try but the point of this article is that it's not its 'own' gravity that is causing the bulge!
And technically within its own gravitational frame of reference the planet does think that it is spherical, it's just that due to the proximity to the star that frame of reference is a bit skewed.
This is similar to the fact that light always travels in a straight line. Any light that 'bends' (lensing/micro-lensing) is actually still travelling in a straight line, it's just that the space that it is travelling through is warped such that a straight line is actually a curve as far as the rest of the Universe is concerned.
Ho, well, within my personal frame of reference I think I am Napoleon, but it doesn't get me much traction with the authorities.
I am confident that a sphere is the solution to x² + y² + z² = C where x, y and z are cartesian coordinates and C is a constant, and this holds even in deep space. The source of the non-sphericity here is tidal deformation of the matter of the quasi-planet, not the gravitational warping of space-time.
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