A Habitable Zone for Complex Life (HZCL) is a range of distances from a star suitable for complex aerobic life. Conventional habitable zones are based on compatibility with water required for bacterial life. Aerobic organism have additional requirements. Different types of limitations preventing complex life give rise to different zones. A planet would need to orbit inside the boundaries of this zone. With multiple zonal constraints, the zones would need to overlap for the planet to support complex life.
Exoplanets
The first confirmed exoplanets were discovered in 1992, orbiting the pulsar PSR B1257+12. Several hundred candidate exoplanets have been identified within convention habitable zones. Most exoplanets are hot Jupiter planets, that orbit very close the star. Many exoplanets are super-Earths, that could be a gas dwarf or large rocky planet, like Kepler-442b at a mass 2.36 times Earths.
Star
Unstable stars are young or old stars, or very large or small stars. Since they are unstable, they have varying solar luminosity, which changes the size of the life habitable zones. These stars also produce extreme solar flares and coronal mass ejections. Thus, life habitable zones require a very stable star like the Sun, at ±0.1% solar luminosity change. Finding a stable star, like the Sun, is the search for a solar twin, with solar analogs that have been found. Star metallicity, mass, age, color, and temperature all effect luminosity variations. The Sun, a G2V star, has a mid-range metallicity optimal for the formation of rocky planets. Dwarf stars (red dwarf/orange dwarf/brown dwarf/subdwarf) are not only unstable, but also emit low energy, so the habitable zone is very close to the star and planets become tidally locked on the timescales needed for the development of life. Giant stars (subgiant/giant star/red giant/red supergiant) are unstable and emit high energy, so the habitable zone is very far from the star. Multiple-star systems are also very common and are not suitable for complex life, as the planet orbit would be unstable due to multiple gravitational forces and solar radiation. Liquid water is possible in Multiple-star systems.
Named habitable zones
A conventional habitable zone is defined by liquid water. Habitable zone (HZ) (also called the circumstellar habitable zone), the orbit around a star that would allow liquid water to remain for a short period of time (a given period of time) on at least a small part of the planet's surface. Thus within the HZ, water, (H2O) is between and temperature. This zone is a temperature zone, set by the star's radiation and distance from the star. In the Solar System the planet Mars is just at the outer boundary of the habitable zone. The planet Venus is at the inner edge of the habitable zone, but due to its thick atmosphere it has no water. The HZ includes planets with elliptic orbits; such planets might orbit into and out of the HZ. When a planet moves out of the HZ, all its water would freeze to ice on the outside of the HZ, and/or all water would become steam on the inner side. The HZ could be defined as the region where bacteria, a form of life, could possibly survive for a short period of time. The HZ is also sometimes called the "Goldilocks" zone. Continuously habitable zone (CHZ): a zone where liquid water can exist of the entire lifetime of a star. Another variation, CHZ2, is a zone where liquid water would be available for . Conservative habitable zone: a zone where liquid surface water remains on a planet over a long time span, as on Earth. This might also need a greenhouse effect provided by gases such as CO2 and water vapor to maintain the correct temperature. Rayleigh scattering would also be needed. Optimistic habitable zone (OHZ): a zone where liquid surface water could have been on a planet at some time in its past history. This zone would be larger than the conservative habitable zone. Mars is an example of a planet in the OHZ.: it is just beyond the HZ today, but had liquid water for a short time span before the Mars carbonate catastrophe, some 4 billion years ago.
Named habitable zones for complex life Over time and with more research, astronomers, cosmologists and astrobiologists have discovered more parameters needed for life. Each parameter could have a corresponding zone. Some of the named zones include: Ultraviolet habitable zone: a zone where the ultraviolet (UV) radiation from a star is neither too weak nor too strong for life to exist. Life needs the correct amount of ultraviolet for synthesis of biochemicals. The extent of the zone depends on the amount of ultraviolet radiation from the star, the range of UV wavelengths, the age of the star, and the atmosphere of the planet. In humans UV is used to produce vitamin D. Extreme ultraviolet (EUV) can cause atmospheric loss. Photosynthetic habitable zone: a zone where both long-term liquid water and oxygenic photosynthesis can occur. Tropospheric habitable zone, or ozone habitable zone: a zone where the planet would have the correct amount of ozone needed for life. Inhaling too much ozone causes inflammation and irritation, whereas too little troposphere ozone would produce biochemical smog. On Earth, the troposphere ozone is part of the ground-level ozone protection. Tropospheric ozone is formed by the interaction of ultraviolet light with hydrocarbons and nitrogen oxides. Planet rotation rate habitable zone: the zone where a planet's rotation rate is best for life. If the rotation is too slow, the day/night temperature difference is too great. The rotation rate also changes the planet's reflectivity and thus temperature, rotation as altered cloud distributions, cloud altitudes, and cloud opacities.NASA, ntrs.nasa.gov/ The Impact of Planetary Rotation Rate on the Reflectance and Thermal Emission Spectrum of Terrestrial Exoplanets Around Sun-like Stars, Scott D. Guzewich A fast rotation rate increases wind speed on the planet. The rotation rate affects the planet's clouds and their reflectivity. Slowing the rotation rate changes cloud distributions, cloud altitudes, and cloud opacities. These changes in the clouds changes the temperature of the planet. A high rotation rate also can cause continuous, very fast winds on the surface. High rotation rates, coupled with strong Coriolis effects, generates continuous, high-speed winds by enabling the formation of persistent, fast-moving jet streams and atmospheric belts.National Geographic, nationalgeographic.org The Coriolis Effect: Earth's Rotation and Its Effect on Weather Planet rotation axis tilt habitable zone, or obliquity habitable zone: the region where a stable axial tilt for a planet's rotation is maintained.The Moon's Role in the Habitability of the Earth, Georgia State University Research Earth's axis is tilted 23.5°; this gives seasons, providing snow and ice that can melt to provide water run off in the summer.Seasons, Georgia State University ResearchEcliptic Plane, Georgia State University Research Obliquity has a major impact on a planet's temperature, thus its habitable zone.Axis Tilt is Critical for Life, Georgia State, astr.gsu.edu Tidal habitable zone. Planets too close to the star become tidally locked. The mass of the star and the distance from the star set the tidal habitable zone. A planet tidally locked has one side of the planet facing the star, this side would be very hot. The face away from the star would be well below freezing. A planet too close to the star will also have tidal heating from the star. Tidal heating can vary the planet's orbital eccentricity. Too far from the star and the planet will not receive enough solar heat. Astrosphere habitable zone: the zone in which a planet's astrosphere will be strong enough to protect the planet from the solar wind and cosmic rays. The astrosphere must be long lasting to protect the planet. Mars lost its water and most of its atmosphere after the losing its magnetic field and Mars carbonate catastrophe event. Star-Sun's solar wind is made of charged particles, including plasma, electrons, protons and alpha particles. The solar wind is different for each star. Earth's magnetic field is very large and has protected Earth since its formation. Atmosphere electric field habitable zone: the place in which the ambipolar electric field is correct for the planet's electric field to help ions overcome gravity. The planet's ionosphere must be correct to protect against the loss of the atmosphere. This is addition to a strong magnetic field to protect against the solar wind stripping away the atmosphere and water into outer space. Orbital eccentricity habitable zone: the zone in which planets maintain a nearly circular orbit. As orbits with eccentricity have the planets move in and out of the habitable zones. In the Solar System, the grand tack hypothesis proposes the theory of the unique placement of the gas giants, the Solar System belts and the planets near circular orbits. Coupled planet-moon - Magnetosphere habitable zone: the zone that planet's moon and the planet's core produce a strong magnetosphere, magnetic field to protect against the solar wind stripping away the planet's atmosphere and water into outer space. Just as Mars had a magnetic field for a short time. Earth's Moon had a large magnetosphere for several hundred million years after its formation, as proposed in a 2020 study by Saied Mighani. The Moon's magnetosphere would have given added protection of Earth's atmosphere as the early Sun was not as stable as it today. In 2020, James Green modeled the coupled planet-moon-magnetosphere habitable zone. The modeling showed a coupled planet–moon magnetosphere that would give planet the protection from stellar wind in the early Solar System. In the case of Earth, the Moon was closer to Earth in the early formation of the Solar System, giving added protection. This protection was needed then as the Sun was less stable. Pressure-dependent habitable zone: the zone in which planets may have the correct atmospheric pressure to have liquid surface water. With a low atmospheric pressure, the temperature at which water boils is much lower, and at pressures below that of the triple point, liquid water cannot exist. The average surface pressure on Mars today is close to that of the triple point of water; thus, liquid water cannot exist there. Planets with high-pressure atmospheres may have liquid surface water, but life forms may experience difficulty with respiratory systems in high-pressure atmospheres. As pressure increases, gas becomes denser, making it more difficult to move in and out of the lungs, also airway resistance is increased as the viscosity and density of the air mixture is greater thus the higher resistance within the airways.This greatly increases the effort required for breathing.Dranged physiology, derangedphysiology.com Physiological effects of high and low barometric pressure, by By Alex Yartsev, April 4, 2020