A mind-independent morality is one that applies to all species. It is not dependent on humanity, consciousness and opinions. Ignorance and lack of awareness would not affect the immorality of an action. For example, other animals eating each other would be immoral even if they don't understand their actions, what rights are, etc. A human child or teenager taking someone's belongings would be immoral even if the child does not understand what it's doing. Is there a secular philosophy that defends such mind-independent morality? And where would the morals come from?
Utilitarians aim for such, and the basis there is that moral actions maximise net utility (for all beings), and degree of morality relates to degree of maximisation. In practice, utilitarianism covers many different interpretations of what utility, with early thinkers taking up pleasure, or happiness, and later ones increasingly complex and nuanced pictures of utility.
Sam Harris in 'The Moral Landscape' argues there is some unambiguous way of working out a 'landscape' of moral action in relation to something like wellbeing. Honestly though, I don't think it makes sense, as discussed here: Is Sam Harris's view of morality innovating? What philosophers innovated specifics on morality?
Kant in 'Groundwork of the Metaphysic of Morals' claimed to arrive by 'pure' reasoning alone, at what he called the Categorical Imperative:
"Act only according to that maxim whereby you can, at the same time, will that it should become a universal law."
Basically, do-as-you-would-be-done-by; and, a version of The Golden Rule.
But I would question whether this, or any reasoning using language, can be meaningfully called 'mind independent'. Following the Private Language Argument, I would say anything considered 'objective', or to have some kind of transcendent realness, is better understood as intersubjective. Discussed in relation to several examples of moral reasoning here: Is the Categorical Imperative Simply Bad Math? :)
The philosophical concept of 'morality' can only apply to creatures who are capable of conscious choice: aka 'moral agents'. A moral agent must be able to:
- Conceptualize some number of different paths forward from the current conditions
- Evaluate each path forward on one or more dimensions
- Choose from among the various paths and act to achieve it
The 'moral' portion of that process lies entirely within °2, but without the capacity for °1 and °3, that moral evaluation is meaningless.
So, no, what you're asking for doesn't actually exist.
Words matter in framing questions
This question uses the word “moral” in the adjective form, to describe a noun.
The word “moral” has a definition that is inseparable from the personhood of the noun it describes. In an existential application, this constrains the discussion of the propriety of the adjective “moral” to nouns which are persons and have a will. This is limited to humans, by definition.
Fictional constructs may project personhood onto any imaginary construct, such as Thomas Tank Engine or Superman, or The Grim Reaper. These don’t enter into an existential discussion on the morality of their act, as their acts are all imaginary.
In essence, putting the words “mind-independent morality” together merely forms an oxymoron no more sensible than dehydrated water. You are asking if “person-less morality” exists. It does not.