Resonances of the first (pulsar) exoplanetary system ever found

Posted: November 26, 2019 by oldbrew in Analysis, Astrophysics, Maths
Tags: ,

Poster from the NASA Exoplanets Exploration Program’s Exoplanet Travel Bureau [credit: NASA/JPL-CalTech]

Before we start – ‘Pulsar planets are planets that are found orbiting pulsars, or rapidly rotating neutron stars.’

Wikipedia tells us:
‘PSR B1257+12, previously designated PSR 1257+12, […] is a pulsar located 2,300 light-years from the Sun in the constellation of Virgo. It is also named Lich, after a powerful, fictional undead creature of the same name.

The pulsar has a planetary system with three known planets, named “Draugr” (PSR B1257+12 b or PSR B1257+12 A), “Poltergeist” (PSR B1257+12 c, or PSR B1257+12 B) and “Phobetor” (PSR B1257+12 d, or PSR B1257+12 C), respectively.

They were both the first extrasolar planets and the first pulsar planets to be discovered; B and C in 1992 and A in 1994.

A is the lowest-mass planet yet discovered by any observational technique, with somewhat less than twice the mass of Earth’s moon.’

Under the heading ‘Planets’ it says:
‘In 1992, Wolszczan and Frail discovered that the pulsar had two planets. These were the first discovery of extrasolar planets to be confirmed; as pulsar planets, they surprised many astronomers who expected to find planets only around main-sequence stars. […] In 1994, an additional planet was discovered. Additionally, this system may have an asteroid belt or a Kuiper belt.’

So that’s some background, now the numbers which turn out to be straightforward enough, starting with the orbits:
727 A = 18365.474 days
276 B = 18365.564 days
187 C = 18365.531 days

The synodic results are:
727 – 276 = 451 A-B
276 – 187 = 89 B-C
727 – 187 = 540 A-C

So the ratios of 89:451:540 are almost exactly 1:5:6 (which equates to 90:450:540).

The only deviation, so to speak, from 1:5:6 is that B has 276 orbits in the period (just over 50 Earth years) rather than 277 – a very small difference.

  1. oldbrew says:

    The two big planets B and C (aka c and d) are close to a 3:2 orbit ratio.
    Actual = 276:187 whereas 3:2 = 276:184.

    A and B (aka b and c) are even closer to a 21:8 ratio, > 99.65%.

  2. Eric Johnson says:

    Doesn’t this throw a monkey wrench into planet formation? If captured, implies rouge, un-attached planets are ripping through space – source of Dark Mass? Where’d they originate? How old is this system? Obviously can’t get there, but what’s chemical make up and structural similarity of A, B and C? Please add more questions.

    Very strange place, is universe.

  3. oldbrew says:

    Eric – it gets even stranger…

    In 2000, the millisecond pulsar PSR B1620-26 was found to have a circumbinary planet (PSR B1620-26 b) that orbits both it and its companion white dwarf, WD B1620-26. This was announced as the oldest planet ever discovered, at 12.6 billion years old.[5] It is currently believed to have originally been the planet of WD B1620-26 before becoming a circumbinary planet, and therefore, while discovered through the pulsar timing method, it did not form the way that PSR B1257+12’s planets are thought to have.

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