How many planets could be in the Kuiper Belt?

ApJL: 

Motivated by recent measurements of the free-floating-planet mass function at terrestrial masses, we consider the possibility that the solar system may have captured a terrestrial planet early in its history. We show that ∼1.2 captured free-floating planets with mass strictly greater than that of Mars may exist in the outer solar system, with a median predicted distance of ∼1400 au.

To evaluate the expected mass of the most massive captured free-floating planet as a function of the maximum semimajor axis, given the arguments presented in Section 2, we implement a Monte Carlo simulation.

This is an interesting calculation, but the result of ~1 free-floating planet does not have a reported error and seems extremely sensitive to the mass function. Equation 1 gives the mass function of free-forming planets:

The coefficient on the power-law term has substantial errorbars, changing the result of the mass function by up to 75% if alpha ~ 1. Examining alpha as well, the paper reports that alpha ~ 0.96 \pm 0.47, which would have a substantial effect on the value of the mass function. It wasn't immediately clear how this substantial variation affected the number of planets detected. Figure 1 shows the confidence intervals on the mass estimate for a planet of abundance unity, but I wasn't able to immediately grasp how to convert this into an errorbar on the planet abundance estimate. Then Figure 2 shows the cumulative fraction and expected number of captured free-floating planets, but doesn't show the confidence intervals. So overall, it's hard to assess the free-floating planet abundance estimate from their simulations given the huge spread on the parameters. The estimate changes from ~1 to ~3 with a change of binning, which is expected but also highlights how uncertain the estimate and approach are, so it would been interesting to see a more thorough exploration of this.

Phys.org:

A recent study published in the Astrophysical Journal Letters investigates the potential existence of Mars-sized free-floating planets (FFPs)—also known as rogue planets, starless planets, and wandering planets—that could have been captured by our sun's gravity long ago and orbit in the outer solar system approximately 1,400 astronomical units (AU) from the sun.

Scientists currently hypothesize that rogue planets are formed from two scenarios: As part of their own solar system but are then somehow ejected into the cosmos, or they form in isolation. But what is the significance of studying free-floating planets, overall?

After conducting approximately 100,000,000 simulations, the results indicate the potential for the existence of a Mars-sized, or even a Mercury-sized planetary body somewhere in the outer solar system approximately 1,400 AU from the Sun.

Universe Today:

Siraj recommends in his study that future work could include gaining greater understanding of how rogue planets are captured in the first place, along with investigating observational tests to identify where to look in the sky for rogue planets, as well. He also notes how microlensing has become the preferred method in identifying rogue planets based on past studies.

Rogue planet capture is extremely interesting for sure. I'm also super interested in the related phenomenon of JuMBOs (Jupiter-Mass Binary Objects), which are forcing astrophysicists to confront the same tough questions as this study.

Previously on this blog:

• An Earth-sized Planet around an M5 Dwarf Star at 22 pc
• Scientists think they know why interstellar object 'Oumuamua moved so strangely
  

Initial Flash and Spectral Formation of Type Ia Supernovae with An Envelope: Applications to Over-luminous SNe Ia

arXiv:

Over-luminous type Ia supernovae (SNe Ia) show peculiar observational features, for which an explosion of a super-massive white dwarf (WD) beyond the classical Chandrasekhar-limiting mass has been suggested, largely based on their high luminosities and slow light-curve evolution.

In the present work, we suggest a scenario that provides a unified solution to these peculiarities, through hydrodynamic and radiation transfer simulations together with analytical considerations; a C+O-rich envelope (~0.01 - 0.1 Msun) attached to an exploding WD. Strong C II lines are created within the shocked envelope.

The scenario thus can explain some of the key diverse observational properties by a different amount of the envelope, but additional factors are also required; we argue that the envelope is distributed in a disc-like structure, and also the ejecta properties, e.g., the mass of the WD, plays a key role.

Interestingly, the proposed scenario can also be tested for normal (non overluminous) SNe Ia:

Indeed, by combining the expected properties as summarized above, we can comprehensively test this scenario for SNe Ia with intensive observational coverage from the infant to late phases; the present work thus provides one strong motivation for the high-cadence survey and prompt follow-up observation for SNe Ia of various subclasses, especially nearby events that allow longterm monitoring toward the late phase.  

The predicted spectra are shown in Figure 4:

The Force Explosion Condition is Consistent with Spherically Symmetric CCSN Explosions

 arXiv: 

One of the major challenges in Core-collapse Supernova (CCSN) theory is to predict which stars explode and which collapse to black holes...The collapsing core bounces at the nuclear densities and launches the shock wave. If the blast wave overwhelms the collapsing star, the star explodes as a core-collapse supernova (CCSN) explosion (Li et al. 2011; Horiuchi et al. 2011).

we show that the FEC [(force explosion condition)] is consistent with the explosion condition when using actual neutrino transport in GR1D simulations...since most 1D simulations do not explode, to facilitate this test, we enhance the heating efficiency within the gain region.

With small, yet practical modifications, we show that the FEC predicts the explosion conditions in spherically symmetric CCSN simulations that use neutrino transport.