# Thread: Astro-Futurology - how things might look a billion years from now

1. ## Astro-Futurology - how things might look a billion years from now

There ought to be an agreed-upon name for the science of studying predicted future geological and astronomical events. "Futurology" is too vague and lends itself mainly to exploring the human civilization within the few hundred years or so.

Anyway, here in no particular order is a batch of far-future studies on the fate of the Earth, Moon, Sun, and other stuff.

The evolution of habitable climates under the brightening Sun

Wolf, E. T.; Toon, O. B.
06/2015

On water-dominated planets, warming from increased solar insolation is strongly amplified by the water vapor greenhouse feedback. As the Sun brightens due to stellar evolution, Earth will become uninhabitable due to rising temperatures. Here we use a modified version of the Community Earth System Model from the National Center for Atmospheric Research to study Earth under intense solar radiation. For small (≤10%) increases in the solar constant (S0), Earth warms nearly linearly with climate sensitivities of 1 K/(W m-2) and global mean surface temperatures below 310 K. However, an abrupt shift in climate is found as the solar constant is increased to +12.5% S0. Here climate sensitivity peaks at 6.5 K/(W m-2), while global mean surface temperatures rise above 330 K. This climatic transition is associated with a fundamental change to the radiative-convective state of the atmosphere. Hot, moist climates feature both strong solar absorption and inefficient radiative cooling in the low atmosphere, thus yielding net radiative heating of the near-surface layers. This heating forms an inversion that effectively shuts off convection in the boundary layer. Beyond the transition, Earth continues to warm but with climate sensitivities again near unity. Conditions conducive to significant water loss to space are not found until +19% S0. Earth remains stable against a thermal runaway up to at least +21% S0, but at that point, global mean surface temperatures exceed 360 K, and water loss to space becomes rapid. Water loss of the oceans from a moist greenhouse may preclude a thermal runaway.

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https://arxiv.org/abs/0801.4031

Distant future of the Sun and Earth revisited

Klaus-Peter Schröder, Robert C. Smith
(Submitted on 25 Jan 2008)

We revisit the distant future of the Sun and the solar system, based on stellar models computed with a thoroughly tested evolution code. For the solar giant stages, mass-loss by the cool (but not dust-driven) wind is considered in detail. Using the new and well-calibrated mass-loss formula of Schroder & Cuntz (2005, 2007), we find that the mass lost by the Sun as an RGB giant (0.332 M_Sun, 7.59 Gy from now) potentially gives planet Earth a significant orbital expansion, inversely proportional to the remaining solar mass. According to these solar evolution models, the closest encounter of planet Earth with the solar cool giant photosphere will occur during the tip-RGB phase. During this critical episode, for each time-step of the evolution model, we consider the loss of orbital angular momentum suffered by planet Earth from tidal interaction with the giant Sun, as well as dynamical drag in the lower chromosphere. We find that planet Earth will not be able to escape engulfment, despite the positive effect of solar mass-loss. In order to survive the solar tip-RGB phase, any hypothetical planet would require a present-day minimum orbital radius of about 1.15 AU. Furthermore, our solar evolution models with detailed mass-loss description predict that the resulting tip-AGB giant will not reach its tip-RGB size. The main reason is the more significant amount of mass lost already in the RGB phase of the Sun. Hence, the tip-AGB luminosity will come short of driving a final, dust-driven superwind, and there will be no regular solar planetary nebula (PN). But a last thermal pulse may produce a circumstellar (CS) shell similar to, but rather smaller than, that of the peculiar PN IC 2149 with an estimated total CS shell mass of just a few hundredths of a solar mass.

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The Solar system's post-main-sequence escape boundary

Veras, Dimitri; Wyatt, Mark C.
04/2012

The Sun will eventually lose about half of its current mass non-linearly over several phases of post-main-sequence evolution. This mass loss will cause any surviving orbiting body to increase its semimajor axis and perhaps vary its eccentricity. Here, we use a range of solar models spanning plausible evolutionary sequences and assume isotropic mass loss to assess the possibility of escape from the Solar system. We find that the critical semimajor axis in the Solar system within which an orbiting body is guaranteed to remain bound to the dying Sun due to perturbations from stellar mass loss alone is ≈103-104 au. The fate of objects near or beyond this critical semimajor axis, such as the Oort Cloud, outer scattered disc and specific bodies such as Sedna, will significantly depend on their locations along their orbits when the Sun turns off the main sequence. These results are applicable to any exoplanetary system containing a single star with a mass, metallicity and age which are approximately equal to the Sun's, and suggest that few extrasolar Oort Clouds could survive post-main-sequence evolution intact.

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https://arxiv.org/abs/1209.5996

Is the Solar System Stable?

(Submitted on 26 Sep 2012)

Since the formulation of the problem by Newton, and during three centuries, astronomers and mathematicians have sought to demonstrate the stability of the Solar System. Thanks to the numerical experiments of the last two decades, we know now that the motion of the planets in the Solar System is chaotic, which prohibits any accurate prediction of their trajectories beyond a few tens of millions of years. The recent simulations even show that planetary collisions or ejections are possible on a period of less than 5 billion years, before the end of the life of the Sun.

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Large Scale Solar System Simulations

05/2009

As the motion of the planets in the Solar System is chaotic (Laskar, 1989, 1990, Sussman and Wisdom, 1992), a single trajectory of the planet evolutions over 5 Gyr can only be thought as a random sample of the Solar System possible evolution. In (Laskar, 1994), I demonstrated, using the secular equations, that Mercury can reach very high eccentricity, allowing for possible collisions with Venus. This was established by constructing by pieces an orbit leading to very high eccentricity for Mercury. The drawback of the method, is that the secular equations lose their validity close to collision, and there was no probability estimate. In (Laskar, 2008), the same experiment was conducted on 1001 orbits providing these probabilities. I also demonstrated that in a non relativist system, the unstability of Mercury is much larger than in the full GR model. In the same paper, I thus conducted some direct numerical integrations for 10 orbits, without averaging, without general relativity (GR), and indeed, 4 orbits out of 10 lead to very high increase of Mercury's eccentricity, allowing collisions with Venus. Soon after, (Batygin and Laughlin, 2008), presented similar results. Indeed, they had followed my previous paper (laskar, 1994), and could thus construct a solutions by pieces, leading to a collision of Mercury with Venus in less than 5 Gyr, but this was also done with a non GR model that is much more unstable than the full model. It was thus necessary to study the possibility of collisions with a full model, including GR over 5 Gyr. I will report here the results of the very extensive study that we made over 2501 solutions of the full Solar System over 5 Gyr, including GR and lunar contributions, with direct numerical integration, without averaging.

Our Sun. III. Present and Future

Sackmann, I.-Juliana; Boothroyd, Arnold I.; Kraemer, Kathleen E.
11/1993

Self-consistent evolutionary models were computed for our Sun, using Los Alamos interior opacities and Sharp molecular opacities, starting with contraction on the Hayashi track, and fitting the observed present solar L, R, and Z/X at the solar age. This resulted in presolar Y = 0.274 and Z = 0.01954, and in present solar 37Cl and 71Ga neutrino capture rates of 6.53 and 123 SNU, respectively. We explored the Sun's future. While on the hydrogen-burning main sequence, the Sun's luminosity grows from 0.7 Lsun, 4.5 Gyr ago, to 2.2 Lsun, 6.5 Gyr from now. A luminosity of 1.1 Lsun will be reached in 1.1 Gyr, and 1.4 Lsun in 3.5 Gyr; at these luminosities, Kasting predicts "moist greenhouse" and "runaway greenhouse" catastrophes, respectively, using a cloud-free climate model of the Earth; clouds could delay these catastrophes somewhat. As the Sun ascends the red giant branch (RGB), its convective envelope encompasses 75% of its mass (diluting remaining 7Li by two orders of magnitude; 4He is enhanced by 8%, 3He by a factor of 5.7, 13C by a factor of 3, and 14N by a factor of 1.5). The Sun eventually reaches a luminosity of 2300 Lsun and a radius of 170 Rsun on the RGB, shedding 0.275 Msun and engulfing the planet Mercury. After the horizontal branch stage (core helium burning), the Sun climbs the asymptotic giant branch (AGB), encountering four thermal pulses there; at the first thermal pulse, the Sun reaches its largest radial extent of 213 Rsun (0.99 AU), which is surprisingly close to Earth's present orbit. However, at this point the Sun's mass has been reduced to 0.591 Msun, and the orbits of Venus and Earth have moved out to 1.22 and 1.69 AU, respectively they both escape being engulfed. The Sun reaches a peak luminosity of 5200 Lsun at the fourth thermal pulse. It ends up as a white dwarf with a final mass of 0.541 Msun, shifting the orbits of the planets outward such that Venus and Earth end up at 1.34 and 1.85 AU, respectively. These events on the AGB are strongly mass-loss dependent; somewhat less mass loss can result in engulfment of Venus, or even Earth. Our preferred mass-loss rate was a Reimers wind with a mass-loss parameter η = 0.6 normalized from inferred mass loss in globular cluster stars. For reasonable mass-loss rates (0.8 > η > 0.4), the Sun's final white dwarf mass is between 0.51 and 0.58 Msun. The Sun spends 11 Gyr on the main sequence, 0.7 Gyr cooling toward the RGB, 0.6 Gyr ascending the RGB, 0.1 Gyr on the horizontal branch, 0.02 Gyr on the early AGB, 0.0004 Gyr on the thermally pulsing AGB, and 0.0001 Gyr on the traverse to the planetary nebula stage (the last three of these time scales depend sensitively on the amount of mass loss).

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Stability of the Solar System

Leubner, I. H.
12/2008

It is a well established myth that the solar system is stable. The argument is generally based on the fact that the rate of the radiative plus solar wind mass loss of the Sun has a relatively small value of 8.81E-05 (1/Byr = 1/Ma) (radiative: 6.63E-05 (1/By)). Experimental results, e.g., that the Earth is separating from the Sun (10m/100year)(1), put the concept of stability of solar planetary orbits into doubt. An understanding of the stability of the solar system is a critical step towards the understanding of the stability of galaxies and the Universe.(2,3) The stability of planetary orbits, which is the other factor determining the stability of the solar system, has until recently not been modeled.(4) A model is presented which shows that the planetary orbits are weakly bound relative to orbital separation, ranging from 0.6 percent for Mercury to 0.006 for Pluto, and 0.0011 percent for CR105, the furthest reported planetesimal. These values are in the order of solar mass/gravity loss, and as a consequence, the model predicts that the solar system is expanding since its formation. The present separation rate of Earth is calculated to 3.0 m/year. Eventually orbital separation of planets will occur, e.g., at 133.8, 1.30, and 0.23 Billion years for Mercury, Pluto, Cr105, respectively under current conditions. The model shows that Mars was previously closer to the Sun and exposed to higher radiation, and that the transition from water to ice on its surface occurred 3.6 Billion years ago.(4) Predictions of the model are reported for all planets and dwarf planets.

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https://arxiv.org/abs/gr-qc/0511138

Orbital effects of Sun's mass loss and the Earth's fate

Lorenzo Iorio
(Submitted on 25 Nov 2005 (v1), last revised 13 Jan 2010 (this version, v2))

I calculate the classical effects induced by an isotropic mass loss of a body on the orbital motion of a test particle around it. By applying my results to the phase in which the radius of the Sun, already moved to the Red Giant Branch of the Hertzsprung-Russell Diagram, will become as large as 1.20 AU in about 1 Myr, I find that the Earth's perihelion position on the fixed line of the apsides will increase by about 0.22-0.25 AU (for \dot M/M = 2 x 10^-7 yr^-1); other researchers point towards an increase of 0.37-0.63 AU. Mercury will be destroyed already at the end of the Main Sequence, while Venus should be engulfed in the initial phase of the Red Giant Branch phase; the orbits of the outer planets will increase by 1.2-7.5 AU. Simultane- ous long-term numerical integrations of the equations of motion of all the major bodies of the solar system, with the inclusion of a mass-loss term in the dynamical force models as well, are required to check if the mutual N-body interactions may substantially change the picture analytically outlined here, especially in the Red Giant Branch phase in which Mercury and Venus may be removed from the integration.

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https://arxiv.org/abs/astro-ph/0111600

Chaos in the Solar System

M. Lecar, F. Franklin, M. Holman, N. Murray
(Submitted on 30 Nov 2001)

The physical basis of chaos in the solar system is now better understood: in all cases investigated so far, chaotic orbits result from overlapping resonances. Perhaps the clearest examples are found in the asteroid belt. Overlapping resonances account for its Kirkwood gaps and were used to predict and find evidence for very narrow gaps in the outer belt. Further afield, about one new short-period'' comet is discovered each year. They are believed to come from the Kuiper Belt'' (at 40 AU or more) via chaotic orbits produced by mean-motion and secular resonances with Neptune. Finally, the planetary system itself is not immune from chaos. In the inner solar system, overlapping secular resonances have been identified as the possible source of chaos. For example, Mercury, in 10^{12} years, may suffer a close encounter with Venus or plunge into the Sun. In the outer solar system, three-body resonances have been identified as a source of chaos, but on an even longer time scale of 10^9 times the age of the solar system. On the human time scale, the planets do follow their orbits in a stately procession, and we can predict their trajectories for hundreds of thousands of years. That is because the mavericks, with shorter instability times, have long since been ejected. The solar system is not stable; it is just old!

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"Is the solar system stable?" and "Can we use chaos to make measurements?"

Wisdom, J.
00/1990

This paper addresses two questions: "Is the solar system stable?" and "Can we use chaos to make better measurements?" In the first part, a review is presented of the numerical experiments which indicate that the motion of Pluto, and indeed the whole solar system, is chaotic. The time scale for the exponential divergence of nearby trajectories is remarkably short compared to the age of the solar system. In the second part, numerical experiments are presented which indicate that the exponential sensitivity of trajectories to changes in initial conditions and parameters cannot be used to exponentially constrain initial conditions and parameters from trajectory measurements. It does appear through that parameters are better constrained by measurements of chaotic trajectories than might naively be expected.

3. https://en.wikipedia.org/wiki/Timeli...the_far_future

It's Wikipedia, but at least it has footnotes and references to check. Should have put this first, but eh.

And now, the big crash.

https://en.wikipedia.org/wiki/Androm..._Way_collision

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https://arxiv.org/abs/0705.1170

The Collision Between The Milky Way And Andromeda

T.J. Cox and Abraham Loeb
20 February 2008

We use a N–body/hydrodynamic simulation to forecast the future encounter between the Milky Way and the Andromeda galaxies, given current observational constraints on their relative distance, relative velocity, and masses. Allowing for a comparable amount of diffuse mass to fill the volume of the Local Group, we ﬁnd that the two galaxies are likely to collide in a few billion years - within the Sun’s lifetime. During the the interaction, there is a chance that the Sun will be pulled away from its present orbital radius and reside in an extended tidal tail. The likelihood for this outcome increases as the merger progresses, and there is a remote possibility that our Sun will be more tightly bound to Andromeda than to the Milky Way before the ﬁnal merger. Eventually, after the merger has completed, the Sun is most likely to be scattered to the outer halo and reside at much larger radii (> 30 kpc). The density proﬁles of the stars, gas and dark matter in the merger product resemble those of elliptical galaxies. Our Local Group model therefore provides a prototype progenitor of late–forming elliptical galaxies.

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https://arxiv.org/abs/1205.6865

The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun

Roeland P. van der Marel (1), Gurtina Besla (2), T. J. Cox (3), Sangmo Tony Sohn (1), Jay Anderson (1) ((1) STScI, (2) Columbia U, (3) Carnegie Observatories)
(Submitted on 31 May 2012)

We study the future orbital evolution and merging of the MW-M31-M33 system, using a combination of collisionless N-body simulations and semi-analytic orbit integrations. Monte-Carlo simulations are used to explore the consequences of varying the initial phase-space and mass parameters within their observational uncertainties. The observed M31 transverse velocity implies that the MW and M31 will merge t = 5.86 (+1.61-0.72) Gyr from now, after a first pericenter at t = 3.87 (+0.42-0.32) Gyr. M31 may (probability p=41%) make a direct hit with the MW (defined here as a first-pericenter distance less than 25 kpc). Most likely, the MW and M31 will merge first, with M33 settling onto an orbit around them. Alternatively, M33 may make a direct hit with the MW first (p=9%), or M33 may get ejected from the Local Group (p=7%). The MW-M31 merger remnant will resemble an elliptical galaxy. The Sun will most likely (p=85%) end up at larger radius from the center of the MW-M31 merger remnant than its current distance from the MW center, possibly further than 50 kpc (p=10%). The Sun may (p=20%) at some time in the next 10 Gyr find itself moving through M33 (within 10 kpc), but while dynamically still bound to the MW-M31 merger remnant. The arrival and possible collision of M31 (and possibly M33) with the MW is the next major cosmic event affecting the environment of our Sun and solar system that can be predicted with some certainty.

4. kzb
Established Member
Join Date
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https://arxiv.org/abs/1205.6865

The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun

There was an article a few weeks back, using GAIA data. The MW-M31 merger is postponed quite significantly according to that.

5. Originally Posted by kzb
https://arxiv.org/abs/1205.6865

The M31 Velocity Vector. III. Future Milky Way-M31-M33 Orbital Evolution, Merging, and Fate of the Sun

There was an article a few weeks back, using GAIA data. The MW-M31 merger is postponed quite significantly according to that.
Rats. I was hoping for it. That's science, though.

6. https://arxiv.org/abs/1808.01333

Cessation of Volcanism on Earth--Possibilities in near geological future

Varnana.M.Kumar, T.E.Girish, Biju Longhinos, Thara.N.Satyan, Anjana A.V.Panicker
(Submitted on 27 Jul 2018)

The number of active volcanoes and its latitudinal extent is likely to be related to the magnitude of internal heat in rocky planets. A critical value of internal heat may require in these planets to sustain volcanic activity and the decline of volcanic activity since their formation of these planets is inferred to be governed by radioactive decay laws. We find that major volcanic activity in Mars, Moon, Mercury and Venus has ceased when their respective surface heat flux values are within ten percentage of the current surface heat flux value of Earth. The reduction in spatial extent of recent volcanic activity in Venus compared to the geological past is inferred to be part of significant reduction in volcanic activity in this twin planet of Earth. We suggest that the volcanic activity in Earth is also declining significantly since the period of mass extinction of dinosaurs 65 million years ago. It may cease completely within a time span between 19 to 65 million years from now with possible implications in Earth's interior, climate and biosphere.

7. A striking take on a predicted (68% certainty) collision and merger between the Milky Way and the Large Magellanic Cloud, in which the Milky Way--apparently the 98-lb. weakling among giant spiral galaxies--will get the Charles Atlas crash course in galactic body-building and come out as the new King of the Interstellar Muscle Beach. At least, that's how the paper seems to read. Set up your telescope-cameras and get ready for the show, only 2.4 billion years away.

https://arxiv.org/abs/1809.09116

The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud

Marius Cautun, Alis J. Deason, Carlos S. Frenk, Stuart McAlpine (Submitted on 24 Sep 2018 (v1), last revised 27 Sep 2018 (this version, v2))

The Milky Way (MW) offers a uniquely detailed view of galactic structure and is often regarded as a prototypical spiral galaxy. But recent observations indicate that the MW is atypical: it has an undersized supermassive black hole at its centre; it is surrounded by a very low mass, excessively metal-poor stellar halo; and it has an unusually large nearby satellite galaxy, the Large Magellanic Cloud (LMC). Here we show that the LMC is on a collision course with the MW with which it will merge in 2.4 +1.2/−0.8 Gyrs (68% confidence level). This catastrophic and long-overdue event will restore the MW to normality. Using the EAGLE galaxy formation simulation, we show that, as a result of the merger, the central supermassive black hole will increase in mass by up to a factor of 8. The Galactic stellar halo will undergo an equally impressive transformation, becoming 5 times more massive. The additional stars will come predominantly from the disrupted LMC, but a sizeable number will be ejected onto the halo from the stellar disc. The post-merger stellar halo will have the median metallicity of the LMC, [Fe/H]=-0.5 dex, which is typical of other galaxies of similar mass to the MW. At the end of this exceptional event, the MW will become a true benchmark for spiral galaxies, at least temporarily.

QUOTE: "The Milky Way (MW) appears to have been quiescent for many billions of years but its demise has been forecast to occur when, in several billion years time, it collides and fuses with our nearest giant neighbour, the Andromeda galaxy (van der Marel et al. 2012b). This generally accepted picture ignores the enemy within — the Large Magellanic Cloud (LMC)." The whole paper has bits like this, making it an amusing and informative read.
Last edited by Roger E. Moore; 2018-Sep-28 at 12:06 PM.

8. A 2016 paper, appears to be widely referenced in later papers and well detailed, on what will happen when the Sun becomes a red giant (SPOILER: Earth fries).

https://arxiv.org/ftp/arxiv/papers/1605/1605.04924.pdf

Habitable Zones of Post-Main Sequence Stars

Ramses Ramirez, Lisa Kaltenegger (Submitted on 16 May 2016)

Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3,700K to 10,000K (~M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

9. Order of Kilopi
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Something I was wondering about....it looks like Gliese 710 will make an even closer approach than once thought. Does this star have a planet or three?

10. Originally Posted by publiusr
Something I was wondering about....it looks like Gliese 710 will make an even closer approach than once thought. Does this star have a planet or three?
Which source did this come from? I thought I saw something about that, will check later.

11. Originally Posted by publiusr
Something I was wondering about....it looks like Gliese 710 will make an even closer approach than once thought. Does this star have a planet or three?
I don't think any worlds have been discovered around Gliese 710 yet. Found the article.

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https://arxiv.org/abs/1805.02644

An independent confirmation of the future flyby of Gliese 710 to the solar system using Gaia DR2

R. de la Fuente Marcos, C. de la Fuente Marcos (Submitted on 7 May 2018)

Gliese 710 is a K7V star located 19 pc from the Sun in the constellation of Serpens Cauda, which is headed straight for the solar system. Berski & Dybczynski (2016) used data from Gaia DR1 to show that this star will be 13366 AU from the Sun in 1.35 Myr from now. Here, we present an independent confirmation of this remarkable result using Gaia DR2. Our approach is first validated using as test case that of the closest known stellar flyby, by the binary WISE J072003.20-084651.2 or Scholz's star. Our results confirm, within errors, those in Berski & Dybczynski (2016), but suggest a somewhat closer, both in terms of distance and time, flyby of Gliese 710 to the solar system. Such an interaction might not significantly affect the region inside 40 au as the gravitational coupling among the known planets against external perturbation can absorb efficiently such a perturbation, but it may trigger a major comet shower that will affect the inner solar system.

12. The future of the Local Group of galaxies: M31 and M33 will collide, M31 and MW will collide but much later than first thought.

https://arxiv.org/abs/1805.04079

First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33

Roeland P. van der Marel, et al. (Submitted on 10 May 2018)

The 3D velocities of M31 and M33 are important for understanding the evolution and cosmological context of the Local Group. Their most massive stars are detected by Gaia, and we use Data Release 2 (DR2) to determine the galaxy proper motions (PMs). We select galaxy members based on, e.g., parallax, PM, color-magnitude-diagram location, and local stellar density. The PM rotation of both galaxies is confidently detected, consistent with the known line-of-sight rotation curves: V rot = −206 ± 86 km s−1 (counter-clockwise) for M31, and V rot = 80 ± 52 km s−1 (clockwise) for M33. We measure the center-of-mass PM of each galaxy relative to surrounding background quasars in DR2. This yields that (μα∗, μδ) equals (65±18,−57±15) mu-as yr−1 for M31, and (31 ± 19,−2 9± 16) mu-as yr−1 for M33. In addition to the listed random errors, each component has an additional residual systematic error of 16 mu-as yr−1. These results are consistent at 0.8sigma and 1.0sigma with the (2 and 3 times higher-accuracy) measurements already available from Hubble Space Telescope (HST) optical imaging and VLBA water maser observations, respectively. This lends confidence that all these measurements are robust. The new results imply that the M31 orbit towards the Milky Way is somewhat less radial than previously inferred, V tan, DR2 + HST = 57 +35/−31 km s−1, and strengthen arguments that M33 may be on its first infall into M31. The results highlight the future potential of Gaia for PM studies beyond the Milky Way satellite system.

QUOTES: The M33-M31 orbit is interesting for multiple reasons. Observations of M33 have provided evidence for warps in its outer stellar and gaseous disks (Rogstad et al. 1976; Corbelli & Schneider 1997; Putman et al. 2009; Corbelli et al. 2014; Kam et al. 2017). Tidal streams have been detected as well (McConnachie et al. 2009). By aiming to match these morphological features in M33 via simulations, it is possible to constrain the allowed M33 orbits and M31 PM values (Loeb et al. 2005; van der Marel & Guhathakurta 2008). McConnachie et al. (2009) find that the stellar debris around M33 can be formed through a recent (< 3 Gyr ago), close (<55 kpc) tidal interaction with M31.

For the six M31-M33 mass combinations explored in P17, the new velocities unanimously prefer a first infall orbit for M33; a long-period orbit is no longer a plausible orbital solution.

The MW and M31 are still destined to merge. However, both the timing and the impact parameter of the first encounter have increased relative to vdM12b, from Tperi = ~3.9 Gyr to ~4.5 Gyr and R-peri ~31 kpc to ~130 kpc. The larger tangential velocity implied by the average DR2+HST [proper motion] means that a future direct collision between the MW and M31 is less likely....

We then included the dynamical influence of the LMC (Mvir;LMC = 10^11 M-sun) and M33 (Mvir;M33 = 2:5 x 10^11 M-sun) in the orbit calculations, using the Kallivayalil et al. (2013) PM for the LMC and the DR2+VLBA PM for M33. This further delays the MW-M31 encounter time by ~1 Gyr, but decreases the impact parameter by half (~75 kpc)....

The main implication for a first infall M33 orbit is that its stellar and gaseous warps cannot be the result of tidal forces via a close encounter with M31. This also supports the assertions in P17 that M33 must have a satellite population of its own (see Patel et al. 2018, in prep.). Multiple satellite encounters (fly-bys, collisions, mergers) could give rise to these features. Other possibilities include long range tides due to M31 or that the features may be related to asymmetric gas accretion or inflows.

We used the new Gaia PM measurements, combined with the existing measurements, to perform numerical orbit integrations. Doing this backward in time for M33 with respect to M31, implies that M33 must be on its first infall. This is consistent with cosmological expectations, and is similar to what has been found for the LMC orbit with respect to the MW (Kallivayalil et al. 2013). One corollary of such an orbit is that M33’s stellar and gaseous warps and tails cannot be the result of tidal forces via a close encounter with M31. The new measurements imply that the M31 orbit towards the Milky Way is less radial than implied by the HST measurement alone, Vtan;DR2+HST = 57 +35/-31 km s-1. This too is in good agreement with cosmological expectations. This implies that the future collision with the Milky Way will happen somewhat later, and with larger pericenter, than previously inferred by vdM12b.
Last edited by Roger E. Moore; 2018-Oct-26 at 01:28 PM. Reason: remove comma

The Small Magellanic Cloud will eventually cease to exist, as it merges with the Milky Way and it loses it gases.

14. https://phys.org/news/2018-10-astron...by-galaxy.html

Another article on the "slow death" of the SMC.

15. This article is exciting BUT totally ignores considerable research showing all life on Earth will perish as the Sun heats up about 1.0 billion years from now, give or take 0.2 billion. So, whatever happens won't matter.

https://phys.org/news/2019-01-catast...lar-space.html

Catastrophic galactic collision could send Solar System flying into space
January 4, 2019, Durham University

New research led by astrophysicists at Durham University, UK, predicts that the Large Magellanic Cloud (LMC) could hit the Milky Way in two billion years' time. The collision could occur much earlier than the predicted impact between the Milky Way and another neighbouring galaxy, Andromeda, which scientists say will hit our galaxy in eight billion years. The catastrophic coming together with the Large Magellanic Cloud could wake up our galaxy's dormant black hole, which would begin devouring surrounding gas and increase in size by up to ten times. As it feeds, the now-active black hole would throw out high-energy radiation and while these cosmic fireworks are unlikely to affect life on Earth, the scientists say there is a small chance that the initial collision could send our Solar System hurtling into space.

QUOTES: Lead author Dr. Marius Cautun, a postdoctoral fellow in Durham University's Institute for Computational Cosmology, said: "While two billion years is an extremely long time compared to a human lifetime, it is a very short time on cosmic timescales. The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our galaxy, waking up the black hole that lives at its centre and turning our galaxy into an 'active galactic nucleus' or quasar. This phenomenon will generate powerful jets of high energy radiation emanating from just outside the black hole. While this will not affect our Solar System, there is a small chance that we might not escape unscathed from the collision between the two galaxies which could knock us out of the Milky Way and into interstellar space."

[[Wait, aren't we already in interstellar space? Did he mean extragalactic? Or maybe we'd just go in a different orbit around the nucleus. Whatever.]]

original article:

The aftermath of the Great Collision between our Galaxy and the Large Magellanic Cloud
Marius Cautun, et al.
Monthly Notices of the Royal Astronomical Society, Volume 483, Issue 2, 21 February 2019, Pages 2185–2196, https://doi.org/10.1093/mnras/sty3084
Published: 13 November 2018
Last edited by Roger E. Moore; 2019-Jan-07 at 07:00 PM. Reason: oops

16. Same as in previous post: lurid headlines, everyone and everything on Earth is dead two billion years from now.

https://www.livescience.com/64433-mi...-imminent.html

Impending Galactic Crash Could Rip Open the Black Hole at the Milky Way’s Center
By Brandon Specktor, Senior Writer | January 7, 2019 06:31am ET

QUOTES: Fortunately for any descendants you might leave 2 billion years from now, only a few stars inhabiting the general region of Earth's sun will be affected by the merger, the authors wrote. The researchers predicted that any risk to life on Earth is "very unlikely" — and, on the brighter side, the Milky Way's brand-new quasar could actually treat future Earthlings to "a spectacular display of cosmic fireworks," according to study coauthor Carlos Frenk, director of the Institute for Computational Cosmology at Durham.

17. A key, often cited paper from a decade ago.

Causes and timing of future biosphere extinctions

Franck, S.; Bounama, C.; von Bloh, W.
Biogeosciences, Volume 3, Issue 1, 2006, pp.85-92 (03/2006)

We present a minimal model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, biosphere, and the kerogen, as well as the combined ocean and atmosphere reservoir. The model is specified by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. During the entire existence of the biosphere procaryotes are always present. 2 Gyr ago eucaryotic life first appears. The emergence of complex multicellular life is connected with an explosive increase in biomass and a strong decrease in Cambrian global surface temperature at about 0.54 Gyr ago. In the long-term future the three types of biosphere will die out in reverse sequence of their appearance. We show that there is no evidence for an implosion-like extinction in contrast to the Cambrian explosion. In dependence of their temperature tolerance complex multicellular life and eucaryotes become extinct in about 0.8-1.2 Gyr and 1.3-1.5 Gyr, respectively. The ultimate life span of the biosphere is defined by the extinction of procaryotes in about 1.6 Gyr.

https://www.biogeosciences.net/3/85/...-3-85-2006.pdf

18. Probably the worst re-reporting of the news about the LMC collision, making the loss of the solar system a certainty.

https://www.foxnews.com/science/milk...ce-report-says

Milky Way will collide with nearby galaxy, hurtling solar system into space, report says
By Amy Lieu | Fox News

A nearby galaxy will slam into the Milky Way galaxy and send the solar system, where Earth resides, hurtling into space, Forbes reported, citing a journal article in the Royal Astronomical Society.

The impact of the Large Magellanic Cloud (LMC), a dwarf galaxy, could also wake up the Milky Way's dormant black hole, known as Sagittarius A*, the outlet reported, citing the study. The hole would then devour surrounding gas, get 10 times bigger and disperse high-energy radiation, the report said.

19. Two similar papers on exoplanets, climate, and the effects of certain atmospheric gases. Both papers are also directly relevant to the future of life on Earth, as solar forcing (i.e., the gradual increase in solar luminosity and heat) is believed the likely killer of all life on Earth, about one billion years from now.

====

https://arxiv.org/abs/1901.02897

Climate sensitivity to ozone and its relevance on the habitability of Earth-like planets

Illeana Gomez-Leal, Lisa Kaltenegger, Valerio Lucarini, Frank Lunkeit (Submitted on 9 Jan 2019)

Atmospheric ozone plays an important role on the temperature structure of the atmosphere. However, it has not been included in previous studies on the effect of an increasing solar radiation on the Earth's climate. Here we study the climate sensitivity to the presence/absence of ozone with an increasing solar forcing for the first time with a global climate model. We show that the warming effect of ozone increases both the humidity of the lower atmosphere and the surface temperature. Under the same solar irradiance, the mean surface temperature is 7 K higher than in an analog planet without ozone. Therefore, the moist greenhouse threshold, the state at which water vapor becomes abundant in the stratosphere, is reached at a lower solar irradiance (1572 Wm^-2 with respect to 1647 Wm^-2 in the case without ozone). Our results imply that ozone reduces the maximum solar irradiance at which Earth-like planets would remain habitable.

====

https://arxiv.org/abs/1901.02901

Climate Sensitivity to Carbon Dioxide and Moist Greenhouse threshold of Earth-like planets under an increasing solar forcing

Illeana Gomez-Leal, Lisa Kaltenegger, Valerio Lucarini, Frank Lunkeit (Submitted on 9 Jan 2019)

Carbon dioxide is one of the major contributors to the radiative forcing, increasing both the temperature and the humidity of Earth's atmosphere. If the stellar irradiance increases and water becomes abundant in the stratosphere of an Earth-like planet, it will be dissociated and the resultant hydrogen will escape from the atmosphere. This state is called the moist greenhouse threshold (MGT). Using a global climate model (GCM) of intermediate complexity, we explore how to identify this state for different CO2 concentrations and including the radiative effect of atmospheric ozone for the first time. We show that the moist greenhouse threshold correlates with the inflection point in the water vapor mixing ratio in the stratosphere and a peak in the climate sensitivity. For CO2 concentrations between 560 ppm and 200 ppm, the moist greenhouse threshold is reached at a surface temperature of 320 K. Despite the higher simplicity of our model, our results are consistent with similar simulations without ozone by complex GCMs, suggesting that they are robust indicators of the MGT. We discuss the implications for inner edge of the habitable zone as well as the water loss timescales for Earth analog planets.

20. More on the future motions of the three major spiral galaxies in the Local Group.

https://phys.org/news/2019-02-gaia-c...collision.html

Gaia clocks new speeds for Milky Way-Andromeda collision
February 7, 2019, European Space Agency

ESA's Gaia satellite has looked beyond our Galaxy and explored two nearby galaxies to reveal the stellar motions within them and how they will one day interact and collide with the Milky Way – with surprising results. Our Milky Way belongs to a large gathering of galaxies known as the Local Group and, along with the Andromeda and Triangulum galaxies – also referred to as M31 and M33, respectively – makes up the majority of the group's mass. Astronomers have long suspected that Andromeda will one day collide with the Milky Way, completely reshaping our cosmic neighbourhood. However, the three-dimensional movements of the Local Group galaxies remained unclear, painting an uncertain picture of the Milky Way's future.

21. When our galaxy and M31 in Andromeda eventually merge, what will happen to their supermassive black holes?

https://arxiv.org/abs/1906.02982

The future Milky Way and Andromeda galaxy merger

Riccardo Schiavi, Roberto Capuzzo Dolcetta, Manuel Arca Sedda (Submitted on 7 Jun 2019)

According to our current knowledge about physical and dynamical properties of the Milky Way-M31 system, it seems likely that these two galaxies will collide and eventually merge in a time very sensitive to initial conditions. Using the HiGPUs code, we have performed several numerical simulations to study the dynamics of the system, trying to define the role of indeterminacy in the present day observed relative velocities of the two galaxies and the time of the merger. At the same time, we have followed the dynamics of the two massive black holes sitting in the galactic centers, to check (within the space and time resolution limits of our simulation) their relative motion upon the completion of the galaxies merger process.

22. Paper that posits the end of life on Earth once solar irradiance reaches ~6%. This would occur within the next billion years.

https://arxiv.org/abs/1906.03527

The runaway greenhouse radius inflation effect - An observational diagnostic to probe water on Earth-size planets and test the Habitable Zone concept

Martin Turbet, David Ehrenreich, Christophe Lovis, Emeline Bolmont, Thomas Fauchez (Submitted on 8 Jun 2019)

Planets similar to Earth - but slightly more irradiated - are expected to enter into a runaway greenhouse state, where all surface water rapidly evaporates, forming an optically thick H2O-dominated atmosphere. For Earth, this extreme climate transition is thought to occur for a ~6% increase only of the solar luminosity, though the exact limit at which the transition would occur is still a highly debated topic. In general, the runaway greenhouse is believed to be a fundamental process in the evolution of Earth-size, temperate planets. Using 1-D radiative-convective climate calculations accounting for thick, hot water vapour-dominated atmospheres, we evaluate the transit atmospheric thickness of a post-runaway greenhouse atmosphere, and find that it could possibly reach over a thousand kilometers (i.e., a few tens of % of Earth radius). This abrupt radius inflation - resulting from the runaway-greenhouse-induced transition - could be detected statistically by ongoing and upcoming space missions such as TESS, CHEOPS and PLATO (combined with precise radial velocity mass measurements with ground-based spectrographs such as ESPRESSO, CARMENES or SPIRou), or even in particular cases in multiplanetary systems such as TRAPPIST-1 (when masses and radii will be known with good enough precision). This result provides the community with an observational test of (1) the concept of runaway greenhouse, that defines the inner edge of the traditional Habitable Zone, and the exact limit of the runaway greenhouse transition. In particular, this could provide an empirical measurement of the irradiation at which Earth analogs transition from a temperate to a runaway greenhouse climate state. This astronomical measurement would make it possible to statistically estimate how close Earth is from the runaway greenhouse. (2) the presence (and statistical abundance) of water in temperate, Earth-size exoplanets.

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